Depression in him, from how I see it, has nothing to do with it. if it were his depression affecting his sexuality, more often than not it prevents one from actually even wanting to engage in sex in the first place. I don't think his wanting to please you and bring you to O has anything to do with it. You are right to be skeptical, not that I'm saying he's doing something terrible but it doesn't sound accurate.

When it comes to his willingness to please you in that way, it seems to be more related to his desire to do so. It sounds to me like he's being rather self-focused sexually and has taken you for granted. The possible reasons for this may be too many to list. Some things that may affect it would bring up questions, at least for me as to how good your relationship is elsewhere? The closer people are, the more passionate they are about each other will affect how much they are willing to go out of their way to please the other person. I can't answer this here but it's something to ask yourself. Although it's been said females need to feel satisfied and happy emotionally with their partner in order to want sex, it also holds true for males. Although a male can still have sex successfully and climax, even when all those things are not in place, in my experience, if they are not happy with their partner 100% it becomes mechanical and self focused, they will be more focused on their own goal of reaching climax and tend to forget about the needs of their partner. Again, that's just my experience and view.

Without knowing more about how your relationship is, I can't say that is what is happening but it's something to look at.