first real breakup - what helped you?

Hi everyone 
im in my early twenties and a month ago I broke up with my boyfriend of three years. We were each other's first everything and even though I was the one who broke up with him I did it very sadly because I really felt it had to happen (we weren't getting along the same way anymore + we each felt hurt from past communication failures) it still hurt a lot. 
I was doing ok but I found out this week that according to him he hasn't thought about getting back together at all, doesn't think of me that way at all anymore and is already using online apps and dating. I know it's partly my ego that's hurt but finding all this out hurt me a lot more than i expected. it's just hard to know someone that used to love you doesn't anymore, especially after a month !! And even when I felt I was doing the right thing breaking up i do still have feelings for him so it's hard to accept that after one month he's fine and that our past doesn't seem to affect him as much as me.
So...
What helped you the most after a breakup? What mantras or routines? I am just barely able to function/make myself food/ do homework and idk what to do even though I rationally know I'll be ok.. Thank you for any comments 💕