Before I begin, I just want to say that I do not always agree with Sylvester Douglas, Lord Glenbervie's opinions, and there's something about his character that I find unsettling. Nevertheless, as he was a first-hand eye witness viewing Pitt's attraction to Eleanor Eden (Lord Auckland's eldest daughter), his account is more credible than that of others. I much prefer, whenever possible, to cite direct references to events rather than secondary sources, even when I don't necessarily agree with the author.
On that note, in The Diaries of Sylvester Douglas, Lord Glenbervie, Vol. 1, Lord Glenbervie records a weekend visit spent at Lord Auckland's house at Eden Farm, near Bromley in Kent. Pitt was also there. Here's what Glenbervie has to say:
"Nov. 20, Sunday, 12 o'clock, Eden Farm - On arriving here yesterday we found Lord Auckland's carriage ready to carry him to dine at the Duchess of Hamilton's, who has a small lodge in the neighbourhood, in her brother's park. It had been settled that I was to go with him, and we found there Dundas and Lady Jane, Pitt, Mrs Bennet and a Miss Muir, who lives with the Duchess. Pitt had dined and slept here [Eden Farm] the night before, and returned here with us last night after supper. He has been here five days in the week every week for the last two months [so presumably since at least September 1796]. The world supposes he is in love with Miss Eden." 
Then the next day:
"Nov. 21, Monday, 10.30 am, Eden Farm - From Pitt's manner in a walk we took yesterday, his constantly sidling up to Eleanor, and particularly his reluctance to go away and various pretexts for staying beyond an hour when he told us he was engaged, I am now persuaded he is in love and means to marry her [Eleanor]. George Wilson said the other day, on our mentioning the report [that Pitt was intending to marry Eleanor Eden], that he thought there would be great levity in his [Pitt's] thinking of love and marriage just at this critical moment of public affairs. The first reflection raised by this remark was on the almost cynical severity of Wilson's character. But I have since begun to agree with him. How strange it would seem, and how offensive perhaps to the public both in England and Europe, if it was to be known that almost every day since the recess of Parliament the man on whom rests the interest of so many, the fate perhaps of this and future generations, the main burthen of the contest between the Allies and the French, have been spent here [Eden Farm] in idleness and lounging and the Minister's [Pitt] mind chiefly occupied with a passion which employs his thoughts the more from his awkward backwardness to speak, or his yet unsettled resolution on the subject." 
Many others were also persuaded that Pitt was going to marry Eleanor Eden. After a dinner on December 7, 1796, Glenbervie records:
"We dined at the Chancellor's. After dinner Lady Loughborough asked Lady Katherine [Glenbervie's wife] if she believed in Mr. Pitt's marriage; that all Pitt's friends believe it will be a match; that she thinks all very right, except the father-in-law [Lord Auckland]. She added that she had said the other day to Mrs. Drummond (Dundas's daughter), "How long do you think my husband and your father will continue in the Cabinet if this marriage takes place?" There was a good deal of sagacity in the question, enough to indicate the reflections of a greater politician than Lady Loughborough." 
To me, this passage indicates that Lord Loughborough, and perhaps even Dundas, as it will be seen, feared and disliked the idea of Pitt marrying Lord Auckland's daughter. Auckland was not well-liked, and perhaps they worried about the amount of influence Auckland could exert over Pitt if he became his father in-law.
From the same diary entry of December 7, 1796, Glenbervie goes on to reflect about Dundas's uncomfortable silence in Auckland's presence when they were all recently at the Duchess of Hamilton's and Eden Farm:
"When we were at Eden Farm about ten days ago, the conversation turned, at breakfast, on the Dundas's. Lord Auckland said he thought Dundas out of spirits, which Pitt denied having observed. We all agreed that he [Dundas] was never much of a talker. Pitt qualified it by saying, "Never in a mixed company," but added a strong instance where the only company was himself, William Grant (the King's Counsel), and Dundas. He [Pitt] said, after being himself for some time at the whole expense of the conversation, he had stopped and waited to see if either of them would begin any subject and that he literally waited without effect, a dead silence having prevailed for all that time." 
Finally, a further entry of Lord Glenbervie from December 21, 1796 bears out Lord Auckland's tendency for political intrigue. It also alludes to the reservations other leading politicians may have rightly been expressing concerning a potential marital alliance between Pitt and Eleanor Eden. That day, Glenbervie, Auckland, and Mr Lowndes were appointed by Pitt to discuss the subject of Pitt's Poor Bill. Pitt's intention was to move to bring the bill forward in the House the following day:
"While Pitt was out of the room and Lord Auckland remained there tete-a-tete, I asked him if he was going to have the Privy Seal. He said, "I do not know what I am to have. I am of Pitt's opinion that everything comes right in time. We shall all be satisfied if things go right. If they do not, we must share the common fate. I am not impatient...If this Treasuryship of the Navy could be opened it would make an arrangement for us all very easy." I infer from thence that he not only is intriguing for himself to have that office, but that he supposed I was apprised in some degree of some negotiation, or at least some plan of Pitt's respecting it. But I do not think Dundas will easily quit his hold of an office which from so long enjoyment he must consider in a manner as his estate, and I should be very sorry, and should think Pitt very unwise, if he were to urge any arrangement in a manner unsatisfactory to Dundas." 
What can we glean from Glenbervie's observations? He certainly wasn't close to Pitt. He was, however, a direct observer of a small part of Pitt's time with Miss Eleanor Eden, and he had certainly not been alone in his assessment that Pitt was in love with her. After seeing Pitt with Eleanor, Glenbervie goes as far as writing those observations explicitly. Why then, didn't Pitt marry her? Some may conclude that Pitt never married because he was not attracted to women. That in and of itself, especially given the time in which Pitt lived, was not a motivation to stop men from marrying. In fact, marrying would have bolstered Pitt's reputation. It did not necessarily stop others! His health and financial reasons have also been suggested as deterrents. Pitt's pecuniary circumstances were certainly alarming, and that argument holds more weight. To me, some of Glenbervie's journal observations in November and December 1796 seem to bear out the potential argument that any martial alliance Pitt made with Auckland's daughter could have been ruinous to him politically. Dundas and Lord Loughborough seemed to have their reservations of Auckland, and Auckland himself so much as directly states to Lord Glenbervie that he wants Dundas's position (or the Privy Seal). A marriage between Pitt and Eleanor Eden would place Auckland in a position of power and influence over Pitt as he would have become Pitt's father in-law.
The country was in a precarious state, and the war with France was going far from well. Taken in all, Pitt was in a far from ideal position to consider marriage at that time. In the end, on January 20, 1797, Pitt wrote to Lord Auckland notifying him that he wouldn't be marrying his daughter. Pitt was not specific in his reasoning, but if Auckland himself was a major barrier, Pitt would not have disclosed that to him. Although Pitt did not marry Eleanor Eden, and there's no documented references that they ever saw each other again, it does not follow that he didn't love her. Without intending to sound cheesy, maybe love just wasn't enough of an inducement for Pitt.
In my next post, I will be quoting directly from passages of Pitt's initial draft letters to Lord Auckland from when he broke it off with Miss Eden. These draft letters have, to my knowledge, never been published, and they will strike the reader in a vastly different light from the final watered-down letter Pitt sent to Auckland. Stay tuned.
1. Bickley, F. (ed.) (1928) The Diaries of Sylvester Douglas, Lord Glenbervie, Volume 1. London: Constable, p. 98.
2. Ibid, pp. 98-9.
3. Ibid, p. 102.
4. Ibid, p. 103.
5. Ibid, p. 107.