sit down and talk like adults.
honestly, try and remove the idea of love that has been lost.
talk about things you both enjoy doing, just talk. get your heart on the table and allow him to get to that point as well.
when you have connected as friends again and your minds are straight the real reason will come out. then you can work on the problem in the relationship.
from my experience, I have hit that point twice in my life.
The one time was when I cheated on a girl, I realised there was no point in the relationship, but I was not secure enough to admit to my fault, this lead to the relationship dragged on for another 2 years and me cheating more.
The other time it was 100% me getting cold feet, I was having major doubts in myself and the relationship. I did a bit of soul searching, cleared out my head, spoke to my best friend and to my brother, after that, when I got myself together, I sat down with her and told her what I went thought, our relationship got stronger after that.