Girlfriend of 8 years lied to me and had someone else...cant eat cant sleep need help

Finally found some were to express myself...so me and my ex were together for I years a few tough patches break up make ups..but I've been nothing but good to her take her out spend time with her. She always said I was too good for her. So we broke up for like 2 weeks because I noticed a lot of comments from one guy on her fb and asked her about it and she said it was nothing swore it...she told me she loves me just didn't want a relationship rn...and I talked to her expressed my heart out n still nothing so a friend of mine shows me a picture of her and the guy and I confront her..all Hell breaks loose and she has no remorse or nothing her excuse was we weren't together,..fastfoward now she blocks me and I see on the guys page it's him an her hugging him saying thsts his girl...it's killing me because unasked a million times was it anyone else and she swore it wasn't she needed a break but she's messing with this guy I'm really stressing and need advice