I 28F caught my bf 31M lying

My boyfriend lied to me about his past relationship... he told me that he and his ex just took turns staying at each other’s places, but I found out she actually lived with him for a few months. Which is fine but I don't like the lying part. When I confronted him, he admitted he lied because he didn’t want to upset me.

He also admitted he’s lied before because he would think about how the answer would make me feel and would change it so I wouldn't get upset or feel some type of way.

He explained that he avoided talking about his ex because I did say in the past I didn't like hearing about his past relationship (tbf I did ask about it thinking I would be okay, but when I knew I wasn't that's when I stopped it and we moved on from there).

Back to the point.. I just feel so heartbroken even though this feels like such a small lie, but know he's lied before and I don't even know what about... and now says I can ask him anything and he’ll give proof if needed. Idek what to ask... or do??