Leon had noticed you had some trust issues from when you first started dating, 3 years ago. You were obviously not trying to be a problem about it so he didn't let it get to him. Maybe you had a bad relationship before him, it was alright.
But the more you guys dated, the more accusatory you got. Even then, he tried to understand. He worked a lot, and most of the time, you wouldn't legally be allowed to talk to him. He did his best to convince you that he wasn't ever with other women besides coworkers, victims or targets. All of which, were not his type.
But you persisted. And eventually, it did piss him off. He could only take so much of being accusing of horrible things before he got sick of it.
You guys were arguing at his place right now. Of course, you were talking about him cheating, and you took him getting upset as suspicion. Out of pure frustration, and a lot of truth, he eventually just yelled.
"If I'm so untrustworthy, let's just break up!"