My bf wants to have sex with other people

So I knew that my boyfriend is a VERY sexual person to the point it started to gross me out a little and I'm on the opposite end of the spectrum where sex is a product of love (I'm not religious in anyway).

Recently he opened the conversation up for a marriage and having kids and told me that he wants to be with me till the end but doesnt want to have sex with just me. But the thing is, he's not open to an open relationship, just wants some 3 somes and hooking up with other couples; he wants me involved in these activities. Also he doesnt need it to be a frequent thing, just like once in awhile sort of thing.

I love him to death and I would 100000% stay with him if he even if lost all his limbs and would even wait for him if he fell into a coma for 20 years. This is how much I love him but this sexual side of him, I still cannot accept and I am thinking if it's worth it to continue.

I fear that I'll never feel like I'm enough for him and dont want to spend my life with him feeling unwanted and uncomfortable.

Am I being too uptight?