I think I am beginning to come to terms with this issue. Or, perhaps I am just rationalizing in order to feel better (which I am totally okay with).
The thing is, my boyfriend is a very passive person in nearly every aspect of his life. Despite his avid participation in various team sports, he is not a very competitive person. There is nothing "alpha male" about him. In fact, he once told me a story about how he and his friend were both pursuing the same girl that they liked, and even though he was disappointed about it, he backed off so that his friend could get the girl. He will go out of his way to accommodate others and to avoid confrontation. He is just a genuinely easygoing guy.
In most aspects of our relationship, this is a very good thing. But in terms of our sex life, I guess it's not so great for me. I tend to be much more attracted to the more sexually assertive type. If I can't tell that a guy is actively pursuing me, then I tend to lose interest. I'm thinking that this is why I lost my libido after our initial courting phase. I just can't get riled up by someone who is so sexually lackadaisical.
That being said, I do think it is something I can learn to live with. It's not ideal, but with all problems there are ways to adjust and compromise. The idea of passivity certainly explains a lot of his actions, and helps me to understand why he claims to be attracted to me but doesn't act on it as often as I would prefer. And it also explains why I have lost my own drive.
I do think there could be more to it at this point in time, especially when dealing with his current depression, and the fact that we have been beating this issue to death for awhile now. I do still believe that some couple's counseling is in order for us, but at least for now I can understand the situation in certain terms and deal with it accordingly.
Thanks all for reading and offering your advice and support.