I do get a psychic sense of him probably crossing over boundaries. Maybe flirtation but not necessarily cheating. This feels more like a symptom than the core issue. Why does he feel he has to go outside of the relationship? Is there anything you can to strengthen your bond so he won’t have this desire so much? Good questions to ask yourself. Maybe make the improvements you can for a while and see how things go. At some point, you may have to put down the law – put some conditions for the relationship. But first, I would consider doing what you can to make things stronger between the two of you.