3way cuddle

Friend ended up having to spend the night last night and my boyfriend invited her to sleep in bed with us. Worst feeling in the world was to wake up to another female snuggled into him with her head on his chest peacefully sleeping. I wanted to throw up it hurt so bad. He doesn't get why it's such a big deal and why it's so painful for me. I don't even want to see my friend after last night. But I feel like I can't say anything. And he got up arguing with me on top of it. Idk what to do anymore :(