Becoming a better me

Hi everyone, I wanted to share a little bit of what i've gone thru recently. I was with my girlfriend (now ex) for 2+ years and they have been very happy times. I truly loved her and i still do, however i had been dealing with jealousy once she made new friends and started hanging out with them more (we were long distance for a while) and even outside of that sometimes I let insignificant things bother me and caused big fights where I yelled and said things i'm not proud of. eventually she got tired of all the fighting and decided to break up for her own good which i understand. she wanted to stay friends and it's been good so far, we text sometimes and send each other funny things online, i have accepted that the relationship is over and I just want to be a good friend. But we had said, if it's meant to be we could try again in the future but she wants to see that i can truly change and not make empty promises, but for now I definitely need to focus on myself and change for myself not for our relationship. I am looking for advice on how to deal with my emotions better when i am upset, jealous or angry. i don't want to take it out on anyone anymore and i want to learn to stay calm through everything. often after our arguments i immediately regretted them because thinking with a clear mind made me realize it's not worth always picking fights. she was always loyal and never made me question her loyalty so the jealousy was more a result of other people getting to spend so much time with her when i can't because of distance. but now that we aren't together anymore, these challenging emotions don't happen often because i have no one to be jealous about and with friends i'm not as invested enough to get angry. so i am not sure how to work on being a better communicator when things get rough. i truly regret how i treated her and i wish to make it up to her somehow by being a real friend and showing her i can change and i don't want her to always remember me negatively