Stressed out Step mum

Hi out to other stressed out step mums or any other type of step parent who reads this

Why are we the bad guys?
Why does the ex seem to think it is ok degrade you in front of the step children?

So my story is a bit like this ....
I met my partner online (we have been together for 6 yrs)
He has 3 girls and I have 2 kids one of each
I have the younger kids
When we started the relationship he had only partial care of the kids (not by his choice)
I had shared custody of mine so week on week off
Then we started to get serious and his ex started to get pushy about his girls coming to stay week on week off - we thought awesome we could move in together and have shared care of all the kids on the same week and be a family.

This went ok, there were good and bad times with the kids getting to know each other and working out the pecking order. We did a lot as a family camping, day trips etc.
This all changed late 2013 early 2014 my daughter started to have mood issues it was scary she could be quite violent more towards me but sometimes the girls got hurt. Myself and her father didn't sit by and just let it happen we had her in councilling and we had plans at school to help with any behavior issues.

Anyway the girls started to voice their concerns to their mother (which was fine) until she changed the rules
The girls were not allowed to be anywhere near my children for fear of their safety. (At that time we were told it would only be for a couple of months)
This meant we had to change our lives the one thing my daughter enjoyed gone. At this time we were also planning to go to my sisters birthday party down south with all the kids we were going to stop in at the Cadbury facotry and just have a good time and trip - the girls knew this and felt sad they missed out (we weren't stopping them from coming with us) they must of said something to their mother due to a very personal text I received from stating how unfit I was as a mother, and why would I rub this in their faces that they were missing out.
I felt so awesome getting this text when i was just starting a 7 hour drive.
I didn't know it then but I wad heading for a mini break down - everything just really getting to me the earthquakes,  work , worry about my daughter and this very personal attack on my children.
Dont get me wrong I can understand the reason why the ex pulled the girls back from our place. What I don't understand is why is it still so vicious.
The ex of my partner is not a step parent herself so I am sure it must be hard to understand that I don't want to take over the care of the girls I just want to work with her to make the girls lives a little easier
I have always said to the girls I am not their mum, they already have a Mum. I am part of their lives though and I am there for them if they need me.
Sorry back to the story.

Since the split of the kids we have found it is nice having the kids separate weeks we can really focus on the kids care - what is hard though is ever changing rules that come with the girls

We are now allowed to have my kids around the girls but only during daytime and neither lot of kids are allowed to stay overnight when either lot is there.
We have to tell the ex every time my children are over
This will all probably change tomorrow but we can live with this annoyance it means there are times when a set of kids misses out on things
We don't do as many family camping trips with all the kids because it is a nightmare to sort out.  We do try day trips though.

But Now ... just when you think what have I got to complain about I now find out I am called Pig or Piggy by the ex and the eldest daughter of my partner between them. Iam just so hurt by this the eldest and I get on really well.

Why oh why are we the bad guys as a step parent.

Footnote : the ex did the dirty on my partner not the other way round