It seems like he really is hiding something. If you have a gut feeling something is wrong, there probably is, unless you are previously prone to paranoia in your life (which still doesn't rule it out.) In rare cases there can be a lack of libido and interest for medical reasons, but I don't think this is the case here, especially with his odd schedule (coming in late at night, doing things that he isn't tell you about).

I suppose you have already confronted him outright and asked him what's going on? Asked him blank and to the point about what he's up to?

It could be pricey, but you could hire a private investigator. I think it would be worth it. Or, you could do a little investigating on your own. Trust is something that has to be earned and he definitely hasn't earned it.

Until you do find out what exactly is going on, you have the right to withhold from him any rights he has to you as a wife. You don't want to risk STDs because you have no idea what he is doing out there. If he really loved you, he would want you, and would give you compliments no matter what you looked like.

Best of luck to you. It's going to be hard and the truth hurts, but it's the best thing for both of you.