was my ex gf cheating on me or am i overthinking?

okay so some back ground info, me and my ex gf (wlw) dated for around year and some few months. my ex would always make these pranks and jokes abt cheating on me or getting with someone else, at first i would get rlly upset and jealous bc thats obv not something you would joke abt, but she would just end up calling me sensitive and stuff so i just ended up dropping it all and would just stop reacting to her jokes and pranks. also another thing i’d like to add is anytime she would prank or joke with someone else, she ALWAYS showed me and would do it otp with me (remember that). now there was this one other girl, let’s call her blue, and let’s call my ex yellow, okay? so my ex and blue had some classes together and would be seen talking to each other a lot, i didn’t think much of it until my ex would tell me that people were saying how her and blue would make a great couple and how they’re practically already dating, MIND YOU, these people who were saying that were YELLOWS FRIENDS. which they did in fact KNOW me and her were dating at the time. my ex is not amused and is telling me how much it pisses her off and all this and that and i’m just saying that she need to either distant herself to make them stop or just set clear boundaries abt it and tell them it makes her uncomfortable and that this and that. also, keep in mind that my ex has told me she has had a crush on blue before we dated but she told me it was more of a friend crush or wtv. OKAY NOW TO THE JUICY PART. today, i was talking to this guy and he was telling me how he this yellow is distancing herself from him bc they aren’t talking that much and he doesn’t know what to do abt it and he doesn’t know why, im curious and im just like “oh id ask for you but we broke up so i cant” and he didn’t even know me and her were together and he was like “what? you two dated? i thought she like blue” and i shook my head and was like “no but everyone always thinks that, we broke up like a few weeks ago bc we weren’t on the same page anymore” and he’s like shocked, and he says “can i show you something?” and im nosy as hell so i’m like, “yeah ofc”, HE SHOWS ME MESSAGES WITH HIM AND YELLOW, AND ITS OF YELLOW SAYING SHE HAS A CRUSH ON BLUE. i’m shocked, and the time she sent those messages? WHILE WE WERE DATING. now, remember how i said everytime she would joke/ prank someone she would call me or show me? yeah well i didn’t see that and she never told me. now i think its bc the guy didnt know me and her were dating at the time so she thought she could tell him since he’s literally the only friend she has who doesn’t know… but am i just overthinking it and its rlly not that serious and she was joking or am i literally finding out shit i wasn’t supposed to know. i can give more info if you guys want. oh and also she made a candy bouquet for this girls bday and didn’t even give me my gifts so..