Gf of 11 yrs asked to see another man

My gf of 11 yrs asked out of no where to see another man. Saying we are vanilla and wants to experience new things. Not totally surprised by this as in before we met she already had a lot more experience body count wise and was with other people until we really became official. I will say she has been loyal this entire time and I feel I owe it to her as the entire relationship if I last 1 minute it's a good day. I mostly please her orally but I know she's craving a good hard pounding I haven't been able to give her. She started sexing this 6ft5 black guy with a 9 inch and they plan to meet soon. She also plans on pleasing orally which is a rarity for me. I will say it does low key turn me on but idk if I should let it happen or not thoughts