First of all, I am sorry for what you are going through. Going through a breakup like you described is very hard and is kind of like grieving a death. You are not even in love with the girl any more, but you miss the relationship. This is normal!! What you are feeling is normal!! You can't get over the death of a loved one overnight, you won't get over the death of your relationship overnight either. You have to be kind to yourself. By all means go out with friends, keep on showing up to events and living, even though there are sometimes tears and pain. As the days go by, you will feel better and better but its going to take some time. Be gentle and patient with yourself.
If the sadness continues beyond a couple of months, think about
entering therapy. Talking it over almost always helps. Sometimes this can be accomplished with friends, but if not, then seek professional help. There's no shame to that.
Good luck Staveandor and I hope this helps!
PS Welcome to the forum. There are great people here. Very supportive. Join us in the chat rooms as well
Moderator Chronic Pain
Believe in yourself. Be kind to fellow humans and animals. Take time to smell the flowers and the coffee.
And by all means, when you are down, ask me for help. I will be there.