So first, the skin on your butt cheek is too thick for the virus to penetrate, so you aren't at any risk. Skin to skin contact means skin like mucus membranes - mouth to genital, genital to genital and genital to anus. Think the really thin, moist skin.
That said, this guy who would take his underwear off while he has an outbreak, and rub his penis against you, is alarming to me. His responsibility is to not expose anyone. He should keep all parts of his genitals away from all parts of anyone else's. It's really easy to get carried away in the heat of the moment, and end up having sex.
If this is someone you are interested in dating, you should educate yourself about herpes. It's very possible to date someone with herpes and never get it, but the person who has it has to be really responsible, and I'm not sure this guy is.
Is he on daily suppressive medication, like Valtrex?
What is your gender? I can give you transmission stats, though we don't have any for same sex couples, unfortunately. We know that for men who have sex with men, the rates are generally higher than hetero couples, and I can explain that if you'd like to know.
In the meantime, you can read the Herpes Handbook. It's free, and written by one of the world's leading herpes experts - https://westoverheights.com/herpes/the-updated-herpes-handbook/
Please can you answer my question, very worried