Extreme Preventative Measure

I am a straight 20 year old. Sure I have jerked off with guys, but never had sexual physical contact with them.
My girlfriend is 22, and bi.
Because of her very religious upbringing and paranoia about getting pregnant out of marriage she won't take the pill so started have sex with women ...in a safe zone.
Then we met and she after a few dates we ended up in bed in her apartment.
It was in bed she laid down the rules. No vaginal penetration. She would blow me and let me eat her out and was able to ejaculate anywhere over her body and in her mouth...but would only let me fuck her anus.
She has an amazing body and a super sexy whales tail thong tan line. I love getting into her tight anus...she knows how to use her anal muscles to grip and release my cock as I fuck her....Super hot...she finger fucks herself while we fuck and has strong orgasms in sync with my own.
She loves to swallow cum and loves me toe eat her anus out after I have ejaculated in it. Then we kiss.
To top it off, she knows I have always loved fucking pussy, so to give me that pleasure we often have one of her girlfriends in bed with us. She gets off watching me fuck them, and loves them to eat her out while I am fucking them.
It all works for me.