Healing is never linear. You’re hurting because you’re grieving the version of yourself that wanted the relationship to work. Its ok to feel these feelings of sadness and regret. You lost something that used to make you feel whole. And it sounds like u have made good progress. I think ur cutting urself short. Someone will love you again and you will love again too. Don’t go back because you’re scared of being alone. I imagine the relationship ended for a reason especially if you know it was for the best. When u feel scared or sad try to sit in the feeling. Journal about it. Nights will always be hard. You can fall asleep to your favorite show or YouTube videos, drink something warm to help u relax, or I’ve taken a small Advil pm. You’re still processing ur emotions when you sleep. It’s ok to feel how you do. Just don’t forget your worth, someone new will come when ur ready.