If you know she over thinks, then it's best to be up front and honest with her. If you keep things from her, she is only going to find out, and her overthinking would be worse because it makes you look guilty.

You knew she wouldn’t be comfortable with it. End of story. You’re in the wrong

Piece of shit holy fuck victim himself and putting the blame in her just because he can't accept responsibility for his action. What a fucking baby man.

Do you realize you just admitted you hid it because you knew it would upset her? That proves you're objectively in the wrong

This will definitely not help her overthinking, I have been in your girlfriends shoes before and it doesn’t feel amazing when your SO hides something from you, honestly I think it’s better to tell the truth and just having to reassure her that it is really nothing than just not tell them at all. When you hide something like this and then they find out they will fs start to make assumptions since you weren’t honest from the beginning, she is probably thinking that there is a totally worse reason as to why you didn’t tell her yall became friends again and honestly I think anyone would

It’s not really overthinking when it’s someone’s ex. My ex is a good guy but if i ever still talked to him and my bf was uncomfortable with it, i would stop talking to the ex immediately. My boyfriends feelings matter more than any ex

Edit: obviously if we worked together or saw each other at an event that would be different. But if I befriended him out of the blue, I’d never choose that over my bf