Something about me and relationships that just dont combine...

Granted ive been through a 5 year relationship before. It ended with my ex partner stating that they weren't ready for a relationship. Which Genuinely made no sense to me, why wait 5 years to tell me that?

I felt like we were a very healthy and communicative relationship, we did have our ups and downs, but I felt that most was dealt with maturely. I still cant seem to figure out what was wrong with us, i had more then enough love to give, and I still felt our relationship was going strong. But ig to them, they thought the opposite, and I genuinely wish I knew what was wrong. 

Its been several months since we last talked, as they cut contact with me soon after breaking up. Im not fully moved on but yet here I am, Striving for a new relationship that may never come. I fear I can't replace what I had with my ex, and I understand that. But even then I can barely make friends, it almost feels impossible trying to converse and be around other people. I wish I knew exactly what was wrong with me, and what may of caused my ex to leave me.