We were together for 5 yrs and it took him 2 months to move on with my friend

Hi
K so ima try to give u the details without writing tooo much
Met this guy 5 yrs ago and we started dating and going out and we were amazing togeher. Well now im second guessing myself. Anyhow while we were going out he became friends with this girl. I was always insecure and i told him i was and he always told me that nothing between him and her cud ever happen. So i let it be and i was nice to her, said hi and talked to her and stuff. His friends were my friends. Anyhow around 5 months ago i asked him for a break...and a week later he said he wanted to break up....I was devastated...So i fell back on her..at this point me and that girl had become pretty good friends. And so for the past 5 months ive been talking to her abt him and how much i love him and miss him and everything. I i found out yesterday that he and her have been going out for awhile. I read emails, and saw pics and omg i dont know how tooo feel... And funny cuz i've asked her over and over in the past couple of months if there is anything between them...i told her if there is then all she has to do is tell me and ill be out of the way...And i told her ill be more than happy ...but she lied over and over and over again. And he did too. Not only to me but to everyone... Now im thinking that this didnt just happen. They always go out and party together and chill togehter. They work at the same place...so sumthing must have been going on long before we broke up...i mean or else it wudnt have sooooo easy to jump from me to her...I mean 5 yrs in a relationship means sumthing... right??...Like i just wanna go over to his place and punch his sooooo hard right now... I feel like such an idiot for giving ur so much of me for a guy like him....What do u guys think? Are they really forever? Like they started going out in september maybe even august and me and him broke up in july. And right now she calling him her hubby and he's calling her his life...What do i make of that? Is she a rebound? or were they always just in love with each oher and i was just standing in the way. Like i feeellll sooooo stupid because its a given that while i was grieving to her, she was telling him everythingg...things that i rlly didnt want him too know.. ****ing ridiculous.. srry just thinking abt him makes me rlly angryy!!!!!!!!!1 how could he do this... Fine move on with her thats ok...atleast tell me...what do they think im a idiot and ill never find out...I've had a hunch for months now but she kept saying no and i dunno why but i believed her like an idiot.