Am I (F19) overreacting? Please i need opinions

I’m sorry, but I’m kinda doubting my judgement right now and i dont wanna make a dumb decision.

To summarize, I’ve (F19) been seeing a boy (M20) for the last 9 months and while it’s not official yet, it’s implicit we are for real and I’ve stayed loyal.
And i mean, i always told him that since we’re not officially committed he can do whatever he wants, but i told him that if he is serious with me he’d either tell me if he catches feelings for someone else or if he flirts he’d keep it to himself as long as it doesn’t go beyond that.
We are long distance but we know each other irl, we have friends in common. We were each other’s first kiss and first romantic/ sorta sexual experience.
Hes kind of a nerd and seems to have values.

That being said, he studies in another city and used to have two female roommates, now its just one. Im okay with that,i trust him, so not a big deal.
Yesterday we were talking about his day, and he told me “oh no my roomie got mad at me again”. The convo went sorta like this.

Him: My roomie got mad at me again

Me: Why so?

Him: Because im talking to you

Me: So what about it?

Him: Well, i told her im really happy with you and that you’re not toxic and since she is she got mad at me. Coz she’s not like you

(At this point i was like what tf did i just read). Coz like, why would she get mad at him for that and why would she be okay with SHOWING it. Like if she was entitled to do so. It just made no sense in what context that conversation would happen, and idk why would he tell me that as if it was a compliment “yeah she toxic ur not”.

I asked my friends and they agreed it seemed fishy. Except our mutual friend, who told me implicitly that he used to have a crush on them in the past by saying “they’re the kind of girls that get mad when the people simping over them find new people”, so welp, she basically said he had a thing for them in the past. She kinda defended him so i wonder if im actually overreacting or reading more into it.

He’s getting a new apartment and she’s moving in with him, i was okay w it too. Like I didn’t care, but now with all these im like nah fuck that.

TLDR:
Im in a long-distance relationship with my “boyfriend”. He has a female roommate who has gotten mad at him for talking to me. I think it’s strange that she is so invested in his romantic life. Now he is getting a new apartment and his roommate is moving in with him.