Unsure... help??

I’m 19, 20 in 2.5 months, boyfriend is 21. We’re talking about maybe having a 3some. But I have big self esteem issues. It was my idea. Bi-sexual and he’s somewhat into it. My issue is controlling my insecurities. Never been good at it and honestly, he doesn’t make me feel any better about myself.. never get paid attention to, barely have sex and if we do it lasts no more than 5 minutes. (Brutal!!!) don’t get complimented. Talks about how hot girls are in front of me or will check them out as well. It’s to the point where I’ll put my head down and not show my face in public when I see other girls. He loves me, but I’m not sure about a 3 some anymore cause I don’t feel like I’m enough for him anymore. Any advice on how to help...?