Nycindie had a hell of a lot of great points right there. I'd also throw in a few other questions.
1. Does your husband know you'd like MORE from your other partner, and if so, how does he feel about (either this partner or some other partner in the future) co-habitating with other partners in the future?
2. Does your bf know you'd like MORE from him? Him seeming to be satisfied with what you have is different than talking about it and hearing he would/wouldn't like more. Being vulnerable and telling a partner you'd like to see more of them and having them say they are content with what is happening now can be awkward, but if you haven't asked, I think it's better than keeping things to yourself if you are feeling frustrated.
3. If your bf says he would like more frequent contact with you, is it possible that perhaps some day in the future you might move closer to each other (if not in together). Would it address any of your feelings if you could stop in for coffee because he was just a few blocks away? Is that something his other partner's would be comfortable with? etc etc.
I think if you're afraid to ask him some of the hard questions, it's less likely that your relationship would grow past the plateau you feel you are at in your head. I think if you (for ease of wording) would like this "secondary" relationship to grow into more of a "primary" one, that really requires some soul baring honesty about how you are feeling and what you would like from the relationship. Talking about it might help settle the issue either way for you, you may even hear what he has to say and find yourself more content even if nothing can change.
I also wonder about sustaining longer term non life sharing connections, I think I have assumed that they will either fade away or grow into more in time since I have no experience in maintaining them before now. It's going on a year here with my boyfriend and I wonder if I can see somebody once a week for two years? Three? It is new odd territory for me too, so although I am not in a position to want what you want from your relationship, I am very curious about what other advice and responses you get about this subject.
Happiness will never come to those who fail to appreciate what they already have.