I also wonder if Belgian King Leopold I didn't have some influence in preventing a marriage between Princess Alice and the Prince of Orange since he was pretty at odds with the Dutch Royal Family over his new kingdom although the Prince of Orange probably did a lot to discredit himself.
I don’t think King Leopold needed to move in the matter since the Prince of Orange certainly didn’t seem to help himself in the plans for the marriage, suggesting his heart wasn’t really in the matter. It kicked off with a flurry of correspondence between Queen Victoria and her eldest daughter in 1859 when the “P. of O.” was being considered for Alice, although the Queen and Prince Albert thought her too young for an engagement. Writing from Baden, where she was staying with her sister-in-law, the Crown Princess of Prussia wrote that "I am shocked at hearing that the Prince of Orange has been leading a bad life here, gambling and drinking and what not, but I hope and trust that it is not so bad as people say. Queen Victoria responded a little later that "You must not tell her [Alice] anything about the Prince of Orange's procedings (of which I hear sad confirmation)..." and later still, "I fear that the reports about the young O. are not at all exaggerated as I have heard them from people who saw and knew the proceedings at B[aden].-and I fear he is in bad hands and has no example before him." Victoria then wrote that "You know, dear Mama, I am not one to excuse such wickedness.....Therefore you know that I am not excusing the behaviour of the P. of O. only think him rather hardly judged."
It was therefore to the Queen’s “great annoyance” that the Prince of Orange “announced himself for the middle of next month! [January 1860] Papa found it necessary to speak to Alice and without saying too much, just to tell her, that he had not had very favourable reports of him, and that we feared that he was in bad hands........I conclude he can have no matrimonial projects at present, leading the life he does at present.” The Queen was warned by her friend Countess Blucher, “never to leave Bertie a moment alone with the Prince of Orange” and was shown a letter from Queen Sophie that the Prince “does not think of marriage; he is too young, and it would be a misfortune for himself and the wife he might choose”. Despite all this, the “P. of O.” initially made a good impression especially since he “does not talk readily of his own accord – but he pays great attention to what is said (I mean when Papa talks at breakfast etc. about politics and military matters......Poor young man he is much to be pitied...” However, towards the end of the visit, “We had a large dinner for the Prince of Orange last night – who was very dull – and positively rude to Alice, which is really very wrong; she feels it just as she ought, and it has settled her feelings about him – which never were favourable, I think. I fear that nothing good will come out of him, which I am sorry for.”
However, by 1861, the Prince of Orange did not appear to have changed his ways and had fallen very low in Queen Victoria’s estimation, as she wrote to her daughter that “I am vexed to hear people defend that odious Prince of Orange – for they may try to bring him over – and propose him for Lenchen, and whatever other parents may do and think – we never will give one of our girls to a man who has led a life like that young man has done!” In 1862 Lady Augusta Bruce, who had a soft spot for the Prince of Orange and was a great favourite with all the royal princesses and princes, wrote that “I believe the Q[ueen] is quite justified in being so hostile to the idea of a marriage with the P. of Orange. It is a great pity but....it really can not be thought of.”
Clearly the Prince of Orange could not pull himself together to reform himself sufficiently and make an effort to win over either Alice’s parents or Alice herself, and while it is a pity that essentially Alice intellectually outgrew the respectable young prince of Darmstadt she eventually married, it’s not surprising that neither she nor her parents were keen to be associated with a young man or a court involved in “, gambling and drinking and what not” from whom it appeared “nothing good will come out”.