Well I got myself into a similar situation:
It fu.cking sux I tell ya... It just seems so cheap, It truly dissapointed me when my X did the same.
As soon as I found out she was beginning to date some chump coz she needed a company, I went on a rampage. I knew she hadn't slept with him yet so there was still a chance for me to beat her to it. So within few days got myself a new gal and fu.cked her silly.
As much as she had hurt me, I tell ya I never felt any better beating her to the race that she initiated. To make things better, her friends even saw me getting it on with the new gal at the clubs. My X perfectly knows I don't fuc.k around with gals just for the sake of company unlike her
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I personally am not such a cheap person, I respect a good realtionship. I cherish the good moments and give myself and the partner involved respect and the time needed to move on after a break up. However If she wants to disrespect the DJ, she is in for a big surprise.