3 way please help idk what to do!?

I am a pansexual woman. my man regularly likes to ask me to have threesomes. originally he would tell me he only wants to see me with her as he sexes me. but yesterday he mentions how he wants the availability to open up his round of conversation with women so he can allow them into our bedroom on top of the availability to have sex with them as long as I'm okay with it. I have a question for the ladies out here would you be okay with it with you be bothered by him wanting to open the relationship and not form. For me it hurts more and it's harder to think about because I was under the understanding and he only wanted to allow another woman into our bed to watch me with her but he might not be content with just that. he's 21 I know he's young I understand he has these thoughts and desires and I'm 22 I'm young we both don't have to stay tied down for this to be as reality. I don't really know if I should continue in a relationship feeling like I'm holding someone back or like I'm obligated to allow this to happen so he would be satisfied and not get tired of our relationship together. I'm scared because he's been my high-school sweetheart and my first I've tried so hard to continue this relationship with him. I've been trying to regain just a little bit of confidence within myself so that I can be happier in my relationship with him but with so much on my mind now with this situation I'd rather be broken hearted then deal with allowing something I might not be really comfortable with. I'll admit sometimes when I'm home I'm think about if I'm willing to allow something like that to conspire for his sake because I know my own shortcomings and I'm constantly recognizing them within myself so I always in a way and beating myself up for myself to try to improve but I'm just over doing so much for others when they don't seem to do for me. I have no friends left and he's all I have and to let him go would be to be completely alone even though I already feel that right now it would be so much more real when we no longer are together. All I know is whatever I won't do someone might be willing to do for him and I don't really mind because I just want him to be happy but I don't want to expel my own happiness for others anymore😢