Healthy Relationships Support Group
No relationship is perfect. A long-term relationship requires constant effort to understand each other, fix misunderstandings, solve problems and continue to grow as both individuals change and evolve. How we deal with our misunderstandings is the focus of this community. Join us to find support, get advice, and share your experience with your relationship.

But if it's simply a situation where he's just not accepting the reason, then that's an entirely different thing and not about you but about him not liking the answer. Nothing you can really do there.
He just doesn't see it yet.. He is hurt
He may be upset because he feels blind sided by this breakup. You guys were together for 5 years, so it makes sense that he would be hoping for an explanation other than, "I just don't love you and don't want to keep this going anymore if that's how I feel."
If I were in his position I would feel absolutely crushed. It would be devastating to me if a partner of several years suddenly broke up with me and told me they just have never really been in love with me. Part of me would also feel betrayed and used in such a situation.
You have every right to end a relationship if you don't feel that you are in love with the other person. However, the longer you wait to do so the more it will hurt the person you break up with, and half a decade is a long time to wait to break up with someone you don't feel you love.
In your ex's mind he may just be seeking any reason that's less painful than being told you're still not in love with him after 5 years of thinking you were.