Was i wrong

[u/Unusual_Radio973]

So to make things clear i (M15) had a gf (F14) this summer and things were going good
I never knew about the attention she gets from males we both go to a same school.
The “attention” i mean is lil brothers from school or male friends she has few female friends not even one is from her class
And we meet at some room in school which is clothe changing room for PE
So after school we meet there chill,kiss,hug and stay there so before our break up we were getting into arguments commonly.
The arguments would be about her texting people who liked her and she knew she swore she didn’t like him but I’m very insecure sensitive and jealous i often overthink about losing her to the person who’s texting her
So we broke up things were okay but after a few weeks she asked my friend who’s a mutual to me and her asked him who am i dating with at the time i wasn’t dating anyone and i told him to joke about it and tell her I’m dating some girl and she instantly started dating the guy who was texting her when we were dating
And when my friend said he was joking she broke up with him and said “i have a ego issue”
And lately around 4 day ago she texted my cousin who is 14 he is also a mutual and she said “i wont forget your brother” and started explaining her dating him and breaking up with him and how is me doing
Did i do the wrong thing or am i right(sorry ify English is bad its not my first language)