I lost a "friend" in the most shameful way possible
around 2017 to 2018, I met a gorgeous girl on Facebook. she was almost the same height as me, had a gorgeous body, liked videogames and was very nerdy about tech.
we dated for about 5 or 6 months, had the best sex of my life during that period, until one day she called and invited me for some ice cream with her friends, I obviously accepted.
arriving at the ice cream shop, she started greeting me to her friends, and to one of them she just said this (I'll call myself John): "John, this is Leo, my boyfriend"
my face dunked in disbelief, but I tried holding myself just to see where this was going, and after talking to the guy for like 2 hours, just discovered that he is one of the nicest guys I've ever met, and they were somehow dating for 7 years, and I've just been used for sex for 6 months straight, cuz I noticed he was a very short guy for her.
arriving home, my head started spinning, I could not get myself to understand what was happening, I was obsessed with a girl that was using me to cheat on her boyfriend for that long, and the guy (that obviously didn't noticed anything) was a very nice person, I could not keep doing this to him and to myself.
we kept "dating" for probably 1 and a half years, and after the meetup she started saying bad things about him, like he was a bad boyfriend and so on, I did not believe it at all, I kept talking to her boyfriend after the meetup and he became almost my best friend, while I kept trying to distance myself from her.
one day I could not hold it anymore, I had to meet him in person to tell everything that was happening, I burst into tears when he approached me, in fear that he would beat me or something, told him all that was happening, and he just hugged me and said "it's okay".
they broke up, stopped talking to me and him, and 1 day after the breakup, she already started dating another guy, who somehow was one of Leo's friends.
he blocked me on all social media possible, I could not contact him ever again, and I don't blame him.
the question is, should I blame myself for this? I did not had any way to know that she was cheating on her boyfriend with me at the start, she managed to keep everything hidden from both of us, she looked and felt single since the start.
I felt depressed after this and now I just feel bad 9 years later, I'm sorry if this was hard to understand cuz English is not my main language, but I had to take this off my chest...