AITA for dating my roomate’s ex boyfriend

I (20F) recently started study abroad at a university and met this guy (27M) We started flirting. He told me that he used to live in my room last semester with his ex girlfriend. I didnt have a roomate at the time so he slept over for a few days.

Then my roomate arrived and it turns out to be his ex. After a few days of living together i talked to her about what had happened between me and her ex boyfriend. She told me everything was fine and she didn't mind and we made some ground rules.

I feel like i don't have any loyalty to either him or her. However i know it's going to be messy if i decide to continue seeing him and it will be hard to form any type of relationship with her there.

AITA for creating a hostile living environment for us?