How come this guy says one thing when he's drunk and another thing when he's sober about his feelings towards me?

Drunk vs sober . People aren't reliable when drunk, and some aren't reliable when sober either. To decide whether you can trust what someone says, it's best to see if his actions match his words for awhile. Although some think of alcohol as being a kind of "truth serum, " it doesn't function that way. Booze tends to make people say & do things they don't mean the next morning.
Because he's drunk. I assume he is nicer when sober and not so nice when drunk. Alcohol can inflict damage on finances, relationships, careers, health and common sense. If he remembers what he says you have a better chance of solving it. If he can't, he has a serious drinking problem and should get help. When he isn't drinking tell him what you see and feel. If he makes changes you may have a chance, otherwise not.