Clearheaded, when you don’t love someone, it slowly erodes your desire to do anything for that person and will often turn to hatred.
Lets take a typical example: man puts dirty socks on the floor instead of the hamper (my husband uses the hamper LOL). When you love the person, its a minor annoyance. When you don’t love the person, it becomes a bone of contention.
Sure its a silly example, but tack 1,000 of these type of small things and a loveless marriage turns into a hate-filled marriage. Unfortunately, I know a few of those.