Why does my boyfriend think I'm cheating on him?

We have been together for about 3 years and there has never been a trust issue between us before. We are both loyal. For some reason, he has been acting very questioning and suspicious towards me lately. In fact, he even opened my phone and looked at it when I went to the bathroom 2 days ago. I don't know if I did something unintentionally to make him think that. What would you do in this situation?

Why does my boyfriend think I'm cheating on him?
Post Opinion