I had a similar situation - I couldn't get over my ex for a long time, no matter what my friends told me. When we were dating, he was so sweet and caring, my friends liked him and everything. All of a sudden, he left me and I was devastated. Since we were in high school (seniors) at this time, I had to see him everyday for the rest of the year, having fun with other girls.
One thing he asked from me after our break-up was that we stay friends and I agreed - to an extent. We were friends, yes, but I ignored him for quite a few months. I moved away from the room if he was there, I ignored his messages, I didn't even look at him for more than 2 seconds. But slowly, I started talking to him again and we became close friends again...but I still wasn't over him.
Then, I made myself do something drastic, that would change my life. I shifted to another country. High school was over, and I wanted to stay in my home country for university but I thought that won't actually help me, so I moved.
Long story short, after 3 years since we dated, I am over him.
What I'm trying to say is, don't let him hold you back. Your memories may have been sweet, and you love thinking about them, but remember, as much as it hurts, it is not what it was like before. Sometimes, you have to take risks. Delete him from your life for a while, and move on. Slowly but surely, you'll get there.
Go out with friends, take risks and meet new people. Whatever you do, do not let your ex hold you back.
I know this will hurt, and I'm sorry to say, your ex may not be thinking of you in the same way you are thinking about him/her now. Even if things somehow managed to patch up and you guys got back together, trust me...it won't be the same.
Remember, all types of friendships, relationships come and go. Don't stay in one place for too long. :)