<human>: Can you provide a brief overview of the text?

A few months after starting going out we met "Harry" who was a big friend and love interest of my gf's cousin. Harry had no interest in neither, he seemed cool. One day we all went out with Harry and a friend of his who lived in another city and came to visit. My gf's cousin already knew him once. Me and my gf got along great that night with him, he seemed fun. Then he left and I never saw him again, even when we met Harry.

Time passed and after a few months I started suspecting my gf was cheating on me. Things went bad and we started fighting a lot. Eventually she just left and cut all contact with me.

After a few months, I discovered my ex-gf is now going out with Harry's friend and they all hang out with Harry's group. My gut tells me they got together just after they met in front of me. Is it all in my head?
<bot>: We met a guy when going out. A while after we broke she's going out with him. Did she cheated.