My boyfriend cheated

I found out my boyfriend has been cheating on me with a girl who has a fiancé he was supposed to hang out with her last friday an i just randomly up up to his house cause he kept saying he didn't want to hang out an i notice he went to go get a hair cut for no reason at all when i got on his instagram i seem he blocked the girl so i thought that was kind of funny to me so when i got on his snapchat the same girl that was block was on his snapchating talking about how she wants to have sex and do thing to him and him telling her if they gang out to cuddle there wont be much cuddling going on i am heart breaken we been together for 4 years now im sorry i am posting this on here i know how support of this group is i just really need help he try to fix it but it wasnt really fixing he blamed me for his mistake and i found out his grandmother passed away yesterday an he was more heart broken then i am pls can i have strong advice😔😢💔