Would you go along with this? Why does he get so angry when I call her his gf, in your opinion?

We're in a long distance relationship. His patients has ranned out and he has cheated on me several times. He also contracted 2 std's, one which he can't get rid of. I forgave him and told him we can work it out even though I'm a virgin I told him we'll be careful. After I found out he had the std's I just thought he was going to stop having sex and be faithful to me until I got there. I found out he had been lying to me about another female. They have been talking for 5 months now. He said he's just "kicking it" with her until I get there and he wants me to accept that. I also found out she has brain cancer. I just think he's too involved in her life. Not only do have sex. They go bowling, movies, dinner, he's met ALL her family and friends. He gets mad at me extremely mad when I call her his gf. I don't know what to do! I love him but I don't want to deal with that AT ALL!!!!