Bi-curious & boyfriend. Sorry it's long!

So my boyfriend recently told me he would love to see me have sex with another girl. (No surprise considering it's about every guys dream lol) well the thing is, I've been wanting to experience with a girl but didn't want to tell him because I actually thought it would make him upset, turns out he would love it.  So that's the plan. Buut then he said "And then I can fuck you from behind while you eat her pussy" I said HOLD ON right there lol. That's a threesome. And that's different. Considering a threesome but he is not allowed to touch the girl and vise versa & he's completely okay with that. All this was said when he was sober. Later than night we had a couple drinks and we started talking about it again and then he said "shit let me also hit that" and it just got me upset because I told him since the beginning I wouldn't want that. I want to think it was just the alcohol talking. I guess I just need advice  from those that have had experienced something like this before? I think I would go through with experiencing with a girl but not the threesome yet. At least not without boundary rules.