Why do ex’s try and come back into your life after they see you’ve moved on 🙄

Me and my ex have been broken up for a month now I would hear from him here and there but ever since I started dating someone he won’t leave me alone he even asked me last night if I really loved the guy I was with and if I ever thought we could get back together ?! He’s the one who ended things so I completely don’t understand ?? And he’s dating someone ! So wtf 😒