Unregistered

I came on here one time about a year ago maybe a little less and posted anonymously, and I never came back. I know in general swinging is not just about sexual things, but in some cases it can be. And I knwo there may not be anyone able to help but this is the only place I can think of to go! Here's some background. My boyfriend of 4 years brought up the whole open relationship thing about 1.5 years ago. We've talked baout it but I told him that if he ever found someone he wanted to be with that we could discuss it again. the topic had never come up seriously since then. Well he jsut met this girl that is willing to do this. I am not willing to be a part of it because of her age, it's not illegal or anything just too young for me. he has told me that it will all be purely sexual he has told her that(I think that she is too young) He has supposedly made clear to her that it is just about sex. And has told me that I am also allowed to have sex with other people. There are other rules specifically pretaining to us that aren't important to my quesiton also. but he is ot to ever insinuate that they are in a relationship, or let her think that this is about love at all. I am the person that he loves in a way that is toatlly different from anyone else. But I'm not quite sure I'm ready to deal with this. He said I can either deal with it or get out of the relationship but that he really doesn't want to lose me he said that I am allowed to participate in anything and that I could watch if I wanted but i don't really want to...so yeah any advice from anyone?