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

To start off I'm new to posting always have just lurked, but I'm having a rough time so I thought I would post here and see if it helps, also she is 20F and I am 22M. So my girlfriend of 4 years broke up with me and is now dating a co worker of mine that I introduced to her, we were going to buy a house together and we're engaged and this came out of no where and she gave me no real explanation as to why.

 I have talk to some mutual friends and they thought she had changed a lot and don't know why, but then they went out with her and the co worker and they won't talk to me now and I don't know why. The worst part so far is she won't talked to me and her and the guy blocked me on every social media, they've only known each other for little over a week and I just don't understand why or how she could throw 4 years out and not even tell me why, and why won't the mutual friends talk to me anymore?

 Sorry if the spelling and grammar suck I'm on mobile because I can't be at my house because it hurts to bad so I'm staying with a friend.
<bot>: Girlfriend of 4 years broke up with me and blocked me off everything and is dating a co worker and mutual friends won't talk to me now.