Why is it so hard to leave someone when the answer is right in your face as to why you should leave?

When you love or like someone, it takes time to get over them so leaving becomes hard.

I heard someone say that human beings will only do something, if they are uncomfortable enough. They will tolerate mild annoyances, but until they are truly uncomfortable, they will not look for a new job, apartment, significant other.

According to them, you just aren't uncomfortable enough (yet).

its always easier said than done

Because I love them, I am dependent on them, I don't want to be alone, those are some of the reasons I have heard,