Fair point. It was about her using an app called "yubo" to look for parties. Yubo works exactly like tinder, except for people under 18 and is intended to find friends; although it's mostly a place for horny teens to get laid lol. I got upset by this thinking she was cheating on me at first but that was not the case. She gladly let me look through her profile and her messages and there was nothing wrong there. She was just using it to find local parties to go to. Now alcohol is a sensitive topic for me because I've grown up with abusive alcoholic parents, so naturally I don't drink and the thought of her drinking hurts me greatly, so I still wasn't too happy about her using that app, but I will let her because I don't want to be in the way of her life. She told me she doesn't use the app anymore and that there was no big deal. Then I woke up yesterday to see her messaging guys on that app next to me in my bed which I thought was disrespectful. That's what the argument stemmed from. (again, she is not cheating on me)

Her telling me I feel like a different person now goes back a bit further though and she has told me that before.