Advice!

How does everyone feel about a threesome with significant other?!?!

My boyfriend and i were randomly talking about spicing up our sex life a bit. We have been dating 2+ years already & we jokingly started talking about threesomes. Well thinking it was a joke it actually turned into a serious conversation! We both genuinely thought long and hard about it, he stated that he would feel more comfortable doing it with another girl instead of guy bc in reality before him, i was already dating women so it wouldn’t be anything new to me!

But I’ve never had a threesome before and I’m super territorial over him. A part of me feels like trying this would be fun and just say i did it yaknow!

But another part of me is telling me it’s a terrible idea! At the same time i want to do it, but then again I’m scared

Help! I feel stuck!