As I tell anyone who is considering an open relationship. First you can't ever undo the deed nor unsee what has been seen. You have to live with the consequences. Sometimes it is a huge amount of guilt as it was for me during my affair. Sometimes it could lead to the end of the relationship because of either the jealousy or if you really loved me you wouldn't want to share me.
Be careful as you move forward. Make sure both of you truly want this and neither is doing it just to please the other one. I assure you if your partner is doing it only to please you than resentment will build up harming the relationship. Please watch the videos of group sex and discuss your wants and desires so you both fully understand each other's expectations. Leave nothing to chance or guessing what the other really wants. You may just want her to go out with another man, come home and tell you all about it but she thought you wanted her to be the entertainment at a friend's bachelor party. If there are any limits discuss them ahead of time such as bareback or condoms only. Communication ahead of time is the key to making it work.
As you start down this road it may feel like trying to line up the moon and stars but seriously if you get it right from the start than you will find open relationships to be the best thing ever BUT going into it without being prepared can be the biggest mistake of your relationship. Personally I love being the extreme slutwife that I am today but it came with time and after paying the price of an affair and a lot of heartache.
Good luck. I hope it goes smoothly for you both.