<human>: Summarize the given text in a few sentences.

(This is a friend posting through my account) 

My mother (F36) and stepdad (M33) have been together for 14-15 years so I've always asummed they are a 'strong' couple. However they're not married and have never ever considered the idea. The only intimate interaction I've ever seen between them is a peck on the lips. This has always been my view of what a relationship is, alongside this in arguments I have been used as a pawn by my stepdad to - what I would now see as - mentaly abuse her. But I'm not sure?

Example: during an argument when I was around 8 he got her to tell me that she had cheated, she came balling her eyes out and did. I hated her for ages for doing this. 

Also in another argument  when I was older around 10 i was told that my grandfather was not my biological grandparent, this shock me as he said she was lying to me and that it wasnt fair. 

Throught it all i have heard constant abuse on both ends with ever swear in the book used at eachother in front of me, these break outs can be triggered over a tv channel or whos turn it is to do the washing up. The worst and most mortifying thing i have witnessed during the constant hatred is when my mother slapped my stepdad (i didnt witness this) he came upstairs to 'ask' me if there was a handprint on this back that she had left, to which i no realise he was just showing me.

Upon discussing some of my issues with my family (on my biological fathers side) it has been asummed that they will break up when i move out as there is not middle man.

I never worried about this when i was younger (apart from the real bad accurences ie the hitting) as it was normal to me but after being in a relationship myself for over 2 years I notice the flaws and cracks in theirs and im a little scared.
<bot>: Can I do anything to help my parents? Is their relationship normal/inevitable for all relationships? Is it my fault they are staying together?