i am sorry to say what i am about to, but i feel it needs to be said.
If someone cheats once, they will do it again. I was engaged to my exfiancee for two years. I then found out he had cheated on me 8 times. and one of those times was with my cousin who was 14, and it had been going on for over 12 months.
You need to decide... coz i guarantee that every time he leaves, or is late, or is anyway out of the normal you will put yourself through hell.