What would you do if your girlfriend started lezzing out right in front of you?

My girlfriend brought her girlfriends to my house. I went out to run some errands, and when I came back, somehow they were both naked and in the middle of some intense lesbian play! I didn't know they had such a relationship. While I was sneaking a peek at them, my dick was completely shot! They suddenly appear on the scene and start a threesome together!