Hello Hushed,
He's not imagining this. As a husband on suboxone I concur with fisherman and can tell you the sub has definitely cut into my sex drive considerably. The good news is that recently I tapered from my 16mg per day dose to 4mg per day, and ALL the sub side-effects have decreased significantly.
As a normal healthy woman, you deserve and need to have sex in your marriage, in your life, and though your husband is doing a positive, responsible thing by taking his suboxone, no doubt something needs to change. Ask him to talk to his doctor about the problem, and inquire about supplements or new drugs that may be helpful. Both of you will be much happier. You may need to push him along, as with my own experience with the sub, the fact that I didn't feel like having sex meant that it didn't feel like a problem for me personally that I wan't having it, but I knew my wife felt differently and that I had to get on the case for her sake, for our sake. Sex isn't the only thing in a relationship, but as you know, without it many other things tend to start falling apart.
All hope is NOT lost, so don't despair. Do your research, talk to the doctor and start trying things.
peace,
octomon