The truth is, the cats already out of the bag. She picked you. The relationship has now changed forever. You have to be wired a little different to ignore that now. It’s what happens afterwards between them that is the question. Insecurities, Jealousy are real experts at finding the cracks in your armor.
I’m sure you’ll have a fantastic time! I’m sure you’ll do everything to please her. It’ll be enthusiastic and exhilarating. And he will see his girlfriend being pleasured and he may say “you don’t act like that with me…” “ You’ve been wanting to f**k him the whole time” “Are you meeting him in secret?” You know, the basics.