Kid and X butt sniffing parents are pathetic.  Do not tolerate that crap in your mate. 

I wouldn't.

Go full frontal zero tolerance on that crap.  Far better to have limited interface with his kids while demonstrating to them a man of confidence and integrity than to sniff their butts and their mommy's butt.

Oh, Rocky,

The injustice of those criticisms by SD’s mother must be galling! Particularly since you made a special effort to provide the girl with her desired eats as well as paying her for dog-sitting. Clearly, the BM is basing her ‘bad dad’ accusations on information provided by her daughter. 

Your SD is an ungrateful, spiteful young whiner, hoping to provoke sympathy from her mother while throwing dad under the bus and, simultaneously, telling BM what she wants to hear. What a shame, that your partner refuses to accept the glaring facts of his daughter’s betrayal and lack of integrity.

Good enough to be taxi driver to a party but still a crappy dad.  This does not compute.  

"He said there was a bunch of other stuff but didn't tell me."

That's even worse than telling you. "A bunch of really bad stuff was said but i'm not going to tell you." I guarantee what i imagine will be worse than whatever he is keeping! WTF. I hope you have a peaceful time with your friend, and try to de-stress."

The Princess was paid to feed her own dog and she bitches about the food. Waaahh! 

She then started on him saying he is a bad dad and that the kids can't stand him .
. . . I said what do you mean next time. We will have our dog sitter the next time. He said there was a bunch of other stuff but didn't tell me. I  asked him how he can keep putting up with this. He said he can't loose contact with his kids. Now I am yet again the bad guy. Ugh.

He is losing them or has lost them, anyway. My DH used to be scared of BM and catered to the skids, but he did not tolerate that kind of verbal abuse. Slowly, with the help of counseling, DH "manned up" for the most part (he has relapsed at times), but by then, he had ensured that the skids had little/no respect for him. Then they all became furious that suddenly there were boundaries.. Between his early puppet behavior and BM's punishing PAS'ing to try to control DH, everyone got what they feared most--except me. I finally got peace or some semblance of it.  Stand your ground and bring in your petsitter. 
Im glad you went to a friend's to decompress. 

I hope you are able to enjoy your break away and clear your head. 

I really wish your SO would have listened to your therapist.  It is NOT helpful for him to share these things with you.  He trauma dumps the negative things his kids or ex say.. and it must make HIM feel better.. but it is not making you feel better.. 

I don't know if he does it.. and when you don't respond in the stepford way he wants.. he gets to uno reverso and direct his frustration with them.... at you..  so he gets a release.. but you get the proverbial "dog kick"

I don't know... maybe you need to come up with a hard stop speech for him...

"SO, Stop right there...you know that it bothers me to hear your EX and kids have walked all over you yet again... It makes me angry on your behalf and I find it frustrating that you won't stick up for yourself, it always ends in you being mad at ME.. so you need to stop venting to me about them. period.   Either you figure out how to deal with their treatment..or don't.. I can't care about it more than you do."

" he can't loose contact with his kids. "   If he wants contact with his kids. He can take them to McDonald fir a happy meal.  Not in your home.  You have a major DH problem.  His kids and BM are playing him.  He playing a game he can't win.  The end gets move all the time.  It's all about them controlling him.  
I under stand why you want off the crazy train.  Good luck   He will loose it's about how much. He already lost the kids ..does he want to lose you ?    
'He went into another relationship, with you, he must respect you and that relationship..  If he is always going to put his kids first he not ready for a real adult relationship .  It's really sucks you you.   [my new dally catch word ]

A parent's/adult's duty is not to feed their children what the children want to eat, the adult duty is make sure there is food for them to eat.  With this turd spawn and her meddling mommy I would have left a box of ramen noodles on the counter.  Enough for 3 servings a day. Nothing more.

When she is pet sitting she is being paid for a service.  The only reason she had access to what food was in the home is because she also is a spawn of  her father.   There was food, she chose not to eat.  

Her hunger pains are on her. That she cried to mommy is pathetic. That mommy opened her putrid breath hole and cried poor baby is even more pathetic.

smh

Man if he buys her an Uber eats card I would be FURIOUS