Is my boyfriend cheating on me?

He is probably stressed out about some certain issue going on in his life. If I were you I would give him a break and see where things go, then tell him how you feel about your relationship. If he say's he is okay with everything.. however you described that he has gotten distant that confuses me because maybe maybe he is seeing another girl but doesn't want to hurt you. Just tell him be like yea I know the truth hurts but say I'm your girlfriend I should have the right to know whats bothering you... try to be understanding of his position as well : ) good luck sweetie! hope things work out for you