Daughter going through first heart break

My daughter dated my son's best friend. My son tried to tell her it wasn't a good idea because his best friend cheats on every girl he's with. I knew this was gonna end in heart break and I didn't want it to because he practically lives at our house. He just comes over unannounced at all hours of the day and stays for days at a time. I never complain because I know his home life and they never have food or hot water and his older sister is very abusive while his parents just stay drugged out in the damn trailer. I tried telling my daughter it was a bad idea but she dated him and got cheated on. She's been heartbroken. It's her first heart break and I've been comforting her but she's convinced she will never love again. It doesn't make it easier that he still comes around only this time he goes through my son's window and stays in his room. I did try to tell my son that maybe his best friend shouldn't come over for a while but he complained how that isn't fair when she was warned not to date him. So the compromise is he stays in my son's room and doesn't come out and for the most part that's worked. My son hasn't dated yet so this is the first child I'm dealing with a heartbreak and nothing I say makes her feel better. Any tips parents?