You ARE welcome here. You are a BS.
Please don't do anything more for your relationship right now. Do the 180 in the Healing Library (FAQ for BS, #11).
Your WW sounds like she has A LOT of issues to deal with. Regardless of your past history together, she DOES NOT have the right to be inappropriate with the opposite sex, nor does she have the right to use your past ways as her excuse. I am a BS, and I would NEVER inflict this pain on anyone...not even my WH.
Continue to be there for your daughter, but I would put your adoption plans on hold indefinitely. Going through with the adoption is a double-edged sword should things not work out. On the one hand you will end up paying child support for her, which your WW may well take and gamble away and you will have nothing to say about it. On the other hand you won't have any legal rights for visitation/custody. That being said, however, if she wants to continue to act like the irresponsible person she is right now, she may end up leaving your daughter with you a lot, in which case it doesn't matter. I just think that at this time if you pursue the adoption it is going to lead to even more heartache in the future for you. JMO. Not what you need to think about now...I'm just mentioning it so that you put the plans on hold until you find your footing again.
I am so sorry you are here. I really hope that she ends her A and realizes what she has. Words and actions can say two totally different things, and I tend to believe ACTIONS.