Have you tried counseling? Sometimes it's helpful to go by oneself when there are what if's, to help you clarify your own thought processes & counselors deal with this stuff all the time/ so they can guage too probably whether you should be concerned.
Are you worried he may be cheating, or does he just seem not attentive, etc? I know marriage go thru lulls, but if you are worried about his noncommitment to you or disrespect/abuse, that's another thing.
Men are different I think anyways than women but abuse is pretty obvious.
Let us know if we can help you further here.