Imagine 10 inches of black cock cumming in her womb and her telling him that she loves him in front of you. Imagine her wanting to stay with him when you are ready to go home? How does that make you feel? If it makes you feel violent, or if it makes you want to hurt yourself, then this may not be the right time. If it makes you feel anything else, I would go for it.
It was your actions that led you here. I would see where it leads. If you don't participate, it sounds like she may leave you anyway. If you do participate, that may happen, but at least you will have the experience, and it sounds like you want it... If she does leave you in the end, at least you will know if cuckolding is something you want to pursue in the future or not. Make it a fun game for both you and her, and you may come out being in a dream situation.
If you go for it, be sure to take pics and video

Do you have a photo of her you can post?
Good luck.