That's a tough situation to be in...
I think going to a psychiatrist is a very good idea, because it's clear you'll have to make some difficult decisions.
Do you think you have doubts about your marriage because you love this other woman or do you maybe think about her so much because your marriage is troubled?
You say that you have two beautiful daughters. You clearly love them so try to keep in mind that your decisions will affect them too.
I hope you find some clarity. Whatever decision you make, it will be the right one.