I am also in the same boat. I am truly mystified by how one human being can treat another without considering their feelings. I am currently going through a big challenge of letting go of someone who I thought would stand by me. This person was my friend, my confidant, and my safety net. He showed his true colors last week and even though I have apologized for my role in the "fight", he won't even talk to me at all. It's extremely difficult to let go, and I just don't understand why I even care anymore.
I'd like to say I believe in a loving, strong relationship that survives the darkest moments, but I'm not so sure anymore. Maybe I will just get another dog.