
it is reasonable you were upset because of the situation. but you have to remember that if she has never given a reason before to not trust her, you have to consider that as well. sharing this feeling even if you feel it might be unreasonable is still necessary to keep a healthy, communicating relationship!
It sounds like she was being open and honest with you about something she could have not told you about and hid. Unless you had a clear boundary set together about friends, you shouldn’t hold this against her. You should make your boundaries clear and have an open conversation about your feelings and expectations for the future (and ask her to do the same for you)
A month into dating I got a girls number and was planning a hang out but I eventually did tell her I had a gf but then she didn’t want to because she felt attraction between us so we didn’t. I saw this other girl at the bar on New Years and I did tell her I had a gf but I told my gf my feelings came back for her, she looked beautiful, and if we broke up I’d take her on a date and then I snapped her to be nice and tell her it was great to see her.