I learned early on not to date great looking men who can't help flirting. If you are spying on him ( although you do not call it that) you are already in trouble with your relationship. Trust is the glue that hold any relationship together, you may say you "trust" him because you have not caught him engaging in any real unfaithfulness. but your 6th sense is telling you that something is not what it seems. I advised my daughter to find a man who adores you and worships the ground you walk on, loves you and shares a bed with you and he knows all the time where that bed is and he is happy to be there. Some men may not be pleased with my take on life, but if you get good love & trust and say you are committed to this relationship  you are really free to give it right back, a win-win situation for both of you.  I know been married for 34 years.