I know you love this woman desperately. But wait. If she has not even told her husband that 1) she might be bisexual, 2) she wants a relationship with a woman, 3) that she loves you, and 4) she wants both you and him and wants to be polyamorous. That is a lot to talk about for them! I get the impression she hasn't even brought up the subject except in a joking manner yet.
So, please, please wait to move until they have talked and begun to sort themselves out on this issue. It will take time, assuming he decides he is willing to be poly. It could take a lot of time. (There are so many threads here from one half of a couple wanting advice now that their partner has told them they want to be poly - often because they fell in love with another. Read through these - they may be able to give you some perspective.)
IF they work it out to have a poly or open relationship, you are not required to love him. You are not required to be in a relationship with him beyond what poly folks call being metamours (i.e. your partner's partner). It is super helpful if you like and respect him but also not required. (Not liking or respecting him makes things much, much harder though.)
Also, whoa nelly! Tell your potential girlfriend to slow down there! She hasn't even told her husband of the relationship with you. And she wants to make you her wife and has already bought a ring! WARNING RED FLAG LAND!
I am very fearful that neither of you are fully living in reality. You've had this tortured intermittent intense contact. You put her on a pedestal as the only woman you ever really loved. You compare all others to her. Maybe your other lovers were dreadful people, but did they ever have a chance to build a real relationship with you? You haven't seen each other in 9 years, then reconnect on one trip. You are NOT seeing each other as you really are. You are in romantic fantasy land. And as you really are - both of you - is worthy of love. Real love knows the beloved for who they really are - not a fantasy.
Sometimes the fantasy transitions to real, long lasting love. It can happen. But only if you slow WAY down, get to know each other for real - via long distance if you have to - and she sort things out, honorably and respectfully, with her husband.
Otherwise you are in a fantasy that is going to turn ugly and hurt you terribly very soon.