Maybe you’d be better off cutting ties with your ex altogether.
I think it’s normal to remember (at least some) exes fondly and to have a special place in your heart for them. I feel that way about a couple of mine. If you miss specific things about them, I don’t think that’s inherently a bad thing.
About a year or so ago, my iPhone did me dirty and put together one of those slideshows with music that heavily featured an ex who really hurt me, the breakup had a profound negative mental and emotional impact on me and it took a bit to recover. We did not keep in touch, I haven’t seen or spoken to the guy since a few months post breakup and that was years ago. I don’t care how he’s doing and can’t say I wish him well. I didn’t even finish the slideshow, but found myself having weird dreams about my ex for a few weeks, waking up sad and dwelling a bit because of the dreams. I brought it up in therapy and cried in that session, but talking through the emotions coming up for me was helpful.
Any time something is impacting the quality of your daily life — including memories of an ex — you can schedule some time to talk to a therapist. If you immediately jumped into a new relationship, maybe you never really took the time to grieve and need to do that now.