A friend (40F) asked to have a threesome w my bf (37M) and me (27F) and I’m not sure what to do

My bf and I have been together for 3.5 years and we have a really good sex life. Like the title says my bf was hanging out with a friend and she asked him if we wanted to have a threesome. I’ve known for a while that she has a crush on my bf but now it’s officially out in the open. She told him she has a crush on me too but I definitely feel like her crush is much more on my bf. I’ve never had a threesome before and it sounds hot but also I think I would get too jealous seeing my man in another woman. I also think bc she openly has a crush on him it would just end up super messy and I definitely am not down to have an open/poly relationship. Has anyone had a threesome in their relationship and did it work out for you? Was jealousy an issue at all? My bf is leaving the decision up to me bc he thinks it would hot to see me getting extra attention but also understands the potential jealously.