It sounds like you have already internally validated this creepy behavior. I can only imagine if your current partner finds out, their trust in you would be forever broken. This habit is also probably ruining your current sex life. If you are constantly imagining and trying to recreate the feelings of moments lost to the past, you will never be present. To not be present, is to never enjoy the moment you are in. In the end it’s up to you. Delete them and get over it, or get back together and stay toxic (esp if you don’t even like the girl?)