Is this a bad thing to try feeling nothing for my ex?
What Girls Said 2
No, this is smart. It's not healthy to keep holding to to feelings for an ex. If this is what you need to do to start moving on then do it. You're not hurting anyone and eventually you'll reach the point where you can think about your ex but realize you don't have feelings anymore. Good luck man.
What Guys Said 1
From a relationship coaching lens, here are my thoughts:
1) I know you said that you've both moved on to new people but that doesn't sound true. You might have a new girlfriend but clearly you're still somewhat into your ex.
2) To directly answer your headline/question, it is not bad to try to feel nothing but it is unhealthy to have feelings for her and simply try to suppress them. Especially, again, since you have a new girlfriend.
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