Hi unknown173628,
Thanks for reaching out!
I've been in a similar situation where I started talking to another guy shortly after breaking up with my ex. Similar to you, I also realized through talking to another guy that I still wasn't completely over my ex and didn't give enough time to completely get past that and heal. I also felt guilt because of that. (Nonetheless, in my case, there weren't as big contrasts between with the new guy being a really great person and my ex being not the best person.)
I feel that you should probably spend some time thinking through your feelings for your ex. Realistically speaking, do you really want to get back together with him? Or is it just to fill the temporary emptiness after breaking up? (I'm assuming somewhat, sorry if this is inaccurate) It sounds like you may be better off not going back to your ex, especially when you already think you two won't last anyway, and especially since he seems to have moved on pretty quickly (fucked other girls).
In the meantime, I think you should let the new guy know that you really think he's a great person and that you really like him, but you need some time before you're ready for an actual relationship. If he really likes you, I believe he will understand and you can still stay in contact as friends. With time, especially if you're determined to move on from your ex (assuming that seems like a good choice based on the situation you're describing), you will soon be ready to be with this new guy. Hopefully the new guy will understand you.
Hope this helps :))
-Greenfern
