What can I do to just be friends?

No matter what you FEEEEEL this is wrong until you are divorced, to even talk to a woman who you have feelings for. Throw this other girl out until things are final. Sounds like you and your wife should go get therapy and try. If this does not work then move on. Your wife needs to trust you. Be the better person. So you will always know you did it right with no regrets. Be strong.