HoosierGuy,
It sounds like Satan would that he would have you. You know what is right but are flirting with temptation. Your ability to discern right from wrong will become more clouded as you walk down that path. The common result is justification for your actions or declaration that you are not cut out for the gospel or that religion is just an organization that sets a bunch of rules. What harm can there be when there are two consenting adults? My actions only affect me. The feeling of loneliness and abandonment justify such actions. All are Satan's tactics.
He is the master of deceit. He would have you believe that there is no God, if that will work. He will have you believe that you are not cut out for the gospel, if that will work. He will have you believe that you are too far gone down a path to return, if that will work. He will have you believe that you can repent later, if that will work. He will have you believe that you deserve to find companionship in worldly ways, if that will work. He will have you believe whatever he can so that you will become as he is. Oh...he is good at what he does. When opportunity passes our way to sin and our resolve is dimmed, that is when Satan steps in. Doing the right thing seems fruitless to this point so why not tamper with sin? Selfishness and lack of self discipline sets in. Often times, at that time, our faith is weak and our spiritual nourishment is low.
So....what to do? The choice, of course, is yours. As far taking this girl out to have a good time is not the issue. The issue is the mindset of knowing that you are weak and vulnerable to sin. It sounds as though you have purposely chosen the venue knowing that where you are going is a place of weakness. You, yourself, have set off the alarms. Have courage to do the right thing. You can do it. Take courage, you are a good person who is running into temptation. Be strong. The way back now is easier than down the road. Repentance now is much easier than repentance later.
Remedies for selfishness....is doing just the opposite....service to others....and being grateful. Start with counting your blessings and then seek to serve. Start there.
As for taking out the girl. Remember, she is recently divorced and has kids and a low paying job. She wants someone to treat her the way the Savior would. That is the best birthday gift you could give her. Her values are higher than yours? Don't let her vulnerabilities and your vulnerabilities lower the bar. She deserves that...as do you.
I am currently undergoing the process of repentance. The hardest part is having a truly repentant heart and feeling the weight and magnitude of what I have done. Spiritually feeding myself feels impossible. But I must stop making excuses and turn. Consistency is key. Positivity is essential. Those are two things I can have control over. Satan would have that I am inconsistent and negative.
Have courage. You will be glad for it.
A good talk that was suggested to me (even on this site) was from a Women's Week talk (2007) by Brad Wilcox's daughter and himself. Go to the thread "Is there any support system in repenting" and it is one of the posts there.
Best of choices to you. Choose the right. "There is safety in righteous doing."