I am just adding my welcome to the forum, and hope you can get things worked out with your new partner. She should certainly be telling you about things ahead of time, although I understand that you tried DADT (Don't Ask Don't Tell) and found out it didn't work for you (and DADT very often doesn't work). So now you can both make an improvement: you asking, her telling.
I'm somewhat worried about her situation with her husband. Is he really okay with things, or is he just unhappily tolerating it, feeling he has no choice? Are he and she working on improving their marriage? What's in the future for that?
I don't think you should make any big decisions just yet, nor try to force yourself to try anything new unless/until you're sure you feel (preferably better than) okay about it.
I hope your interactions on Polyamory.com help you gain some of the thoughts and insights that could help you. Just reading about the subject can help make it seem less unfamiliar, and thus, perhaps, not so threatening.
Glad you could join us.
Love means never having to say, "Put down that meat cleaver!"