The biggest messes we get ourselves into usually happen when we "should" on ourselves. You know, we expect usually that a married couple "should" have sex, then we expect a married couple to stop having sex at some point, and so on and so on, or whatever. My point is, your relationship is what you make it.
If you and hubby are attempting to make love because you think you SHOULD, well, no wonder it ain't happening!! Most people inwardly rebel at being told what to do, even when it's ourselves who tell us what to do. Can you hear that dialogue in your head? "I really should want to..." "No!"
Last thing I want is to fuck someone just because I think I'm supposed to. If I had a dick, it would go soft!
The other problem is that people tend to stop seeing their partner anew each day. We tend to think that because we've been with someone 10, 15, 20 years, we know them. We think there isn't anything new to discover. So not true! People change and grow and are constantly learning and absorbing new info, no one is stagnant. Isn't it every seven years that our bodies completely regenerate or something like that? So, maybe you guys have just stopped seeing the nuances of who you both really are. You may be just looking and allowing yourself to see only what you expect to see, instead of looking at your mate with a fresh pair of eyes as if you've just met them. It IS possible!
You're not in trouble! It only feels like that when you think you SHOULD be something you're not. You two might just want talk about where you are, what you want, and figure out how to give it to each other. Is it romance? Is it discovering new things about each other? If having sex is a goal, let it happen because you two want it, not because you think it's something that a married couple is supposed to be doing! Be compassionate and think of it as a fun game, nothing to worry about!! Explore each other and what you want, what you feel might freshen up your relationship. Don't get all heavy about it, it can be fun -- think of this stage you're at as a signpost that says it's time to go deeper and find more ways to get to know each other and yourselves.