Should I stop be Mr. Nice guy?
Stop being Mr. Nice Guy. Turn off her cell phone. And if the car she took is in your name, either get it back or have her put it in her name and start making the payments. Who cares if it costs her more in the end? She made her decision, let her deal with the repercussions. It’s time to get real. She’s not coming back no matter what you give her. Her family is nuts and they’re not going to support a reconciliation. Ask her to meet in a public place, just the two of you to split up the property. If she doesn’t show, file for divorce on the grounds of adultery and abandonment (you can show how she was going to leave you for another man, with whom she is now shacked up). You’ve tried being nice and it’s not working. It’s now time to get on with your life and find someone who will care and respect you as much as you care and respect her. Good luck and Godspeed.
