Some womanly support/advice.

Ok so my boyfriend wants to have a threesome which a part of me wants to because I wanna be with a girl but then again I don't because my anxiety part of me keeps feeling like he is bored/tired of me or I am not good enough anymore.... idk if I am just over reacting or what but I have this terrible feeling inside. My stomach just hurts and is turning and my chest hurts it feels like I am breaking...