Why some men stayed in the relationship even though he doesn't love her?

My cousin shared his secret to me. He never love her but he decided to stay with her. They are 6 years in the relationship. I asked him why... he said he doesn't know. He can't break up with her.. He prefer his girlfriend will initiate first. He never cheated her. He said it's find for him if her girlfriend cheated.

I ask why " How do u cope pain"
He said " the advantage of LDR is to numb the pain"

Can you relate with him?
Why some men stayed in the relationship even though he doesn't love her?
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