well i would say if he think that you are cheating on him his just fooling himself. i would say that he may be the one cheating because now he think you know that he does so he say that in order for you to feel sorry and not to even think of him... i can promise you that he may be the one CHEATING..
well what you should ask him who do you cheat with he must prove what his saying right? well if he dont have any proof then his just making excuses of not being with you then...
You have to assure him of your love and make him understand that you couldn't possibly think of another man. Assurance is all that is needed to calm his spirit and hopefully, he'll get over the idea. If he doesn't believe you, let the matter go.
If your not cheating why would you have to try and prove it to him. He maybe the one that is cheating. When a man accuses you constantly and wants to know your whereabouts at all times is because he wants to make sure that he is not in the same area as you.