I was in an 8 year relationship. I had been suspicious for a while but was told it was my own paranoia and insecurities that were the problem. One day, we had an argument and she left her phone on the bed. I knew if I checked any trust we had would be broken by me but I just had to.

Turns out she was cheating on me with my oldest friend. We decided to make a go of it anyway. A year later we broke up. Still hung out a lot though. Complicated reasons why but still spent a lot of time together.

3 years later she tells me shes now in a relationship with said friend. About half my friends all knew this and hid it from me too. Apparently they didn't know the whole time. Probably only around 18 months.

I didn't take it well and acted pretty self destructively. Most of my friends stopped talking to me, some didn't. But I get a lot of talk about how it's on me to heal myself now. Which is true, but also kinda hard not to be affected by the whole thing which kind of put any self worth I had through the floor.