While HIV/AIDs isn't necessarily a death sentence these days I get why the guy was so angry. After all I can only name Magic Johnson whose lived a long time with it.
If someone gave me an incurable STD that could effectively kill me faster than nature intended then I'd probably kill her.
To those people saying "Wrap up" bla bla bla, she was his girlfriend, someone he's supposed to be able to trust. If you're in the position where she's taking other contraceptives then why the hell not go in without a raincoat?
They had only started dating "recently".