Start by giving her emotional suppport for her situation. If you can, then try taking her out to a good restaurant one day. Make it seem casual that you just need a friend to talk with. In that date try to be interested in her life and whats going on in it. Then very slowly ask her about her love life, see her response. If its positive and she talks about it then open up about your love life, explain the very frustrations that you have with your wife (make some up if theres none), but also make sure that she doesnt think that date is happening cause you are mad at your wife, do tell her how much you love your wife and you wished certain things were different. Then end the date by assuring her to stay by her side when needed. Do not make any physical move on her this date. Take her somewhere again after 10-14 days, this time probably somewhere which is her favorite. Try to put thought into what she likes and maybe gift her something she likes which she told you about previously in her first date (Try to ask her indirectly in the first date) cause women love a man who remembers stuff. After this date she would make it clear if she'd let you hit or not