You think she should commit to being your primary partner after some online and phone chatting and a couple dates? I think you 2 have some good vibes and NRE happening, but she's also attracted to her female friend. What she and her gf do with that other guy is their business and shouldnt concern you overly much. You know Andrea likes you. You 2 haven't even had sex yet.
It sounds like you're letting jealousy about what Andrea and her gf might do with the other guy get in the way of what you and A have going. No need to rush into a 3way with a 2nd woman. I'd say just enjoy what you've got and see where it leads.
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve.
~Percy Byshe Shelley