Threesome

Me and my boyfriend have a threesome planned in the next few weeks and i’m so on and off about the subject. I’m bisexual and i think it would be enjoyable but when it comes time and i see my boyfriends hands on her i feel like i will get sick. But since i’ve brought it up my boyfriend is so happy and he gets super excited talking about it. The girl has a better body than I do. Not to mention me and my boyfriend lost our virginities to each other and have only had sex with each other. I’m afraid of the outcome this will have on our relationship.