Thanks for the replies!
I agree that it's not his job to make me happy -- that's not really my intention. I'm just wondering if there's any support that I CAN ask for, and what that is. I am really afraid to express my needs because whenever I do his SO gets upset, because her needs are pretty opposite seeming from mine.
In terms of scheduling in advance, he's made it pretty clear that he's not into that. He's only willing to commit to certain nights of the week, like Mondays, where we could only spend a few hours together (he is only free after 8, and I usually need to go to bed at about 10). If there are events, he's not willing to commit, and that's one big issue -- feeling comfortable going to events.
The other big issue is just feeling unwanted. He also says we have to ask in advance, and doesn't ask us to do anything. So it's a matter of who asks for time first. It just makes me not want to ask for time unless it's really important to me, because I feel like he might commit to something with me when the other girl wants to be with him and I don't want that to happen. And it feels really shitty to have to ask your friend to hang out with you all the time...