If you have to ask this question then either you an overly jealous type or, he has given you good reason not to trust him. If we really listen to our inner selves we seldom let ourselves down. A "feeling" is a signal that we are usually right, but then, we have to prove it to some point. If you think he's cheating then take a friend and follow him, or, if he's a compulsive liar walk out that door and don't look back.
Good luck Marcy