Interestingly, I think Doom actually means it when he's talking wistfully about how he'll miss her. The thing is, why Doom DOES have a sense of honor, and a very strong and unyielding one, it's centered completely around his gigantic ego. You're probably all right if you make a basic deal with him - for instance, during the rare occasions when he's had to team up with the FF, he's sworn to play fair with them until the team-up is over, and he's always kept his word - but anything more elaborate, and you risk him twisting it into some 'letter of the law, but not the spirit' thing. Because factor two regarding Doom is that he is undoubtedly an 'ends justify the means' type. My guess is that, had he found Valeria before this whole thing with the demons came up, he probably would have been perfectly happy to try and pick things up where they'd left off, but the demon thing happened first, and sacrifices must be made. By his way of looking at things, it's perfectly fair - he regards love and compassion as pleasant enough if one gets a chance to indulge in them, but in his life, he rarely does, and he's not going to let them get in the way of his quest for power.