Boyfriend of 4 years came out as gay.

My first love who I was with for 4 years and who I lived with for the last year broke up with me by coming out at gay (were both 20). Has anyone else ever been through something similar? I just feel so confused, rejected and don't know what that means for the entirety of our relationship. Since we broke up a month ago he's slept with a few different men, when I asked him about it he just said it helped him confirm he is gay and made the right choice. I just feel so inadequate and hurt.