Your X and his 'woman' are awful. They are textbook what you should not do to a child.
Does your son remember the times you drove out to meet his dad and he was not there? Maybe bring those up, and say that his dad must have forgotten. Say, he must be very forgetful.
As far as what the ho calls you, tell your X that this is totally unacceptable. what do you say to him when he uses bad language? We call it potty mouth. Just say, maybe she does not know that this is potty talk. Maybe her mother did not teach her that.
Don't worry too much about what your son learns over there about you. It must be confusing, but deep down he knows you are the one who loves and supports him. Give him some time when he comes back from a visit to make the transition. My kids don't even come in the house right away, they have to spend some time outside first, then they can make the mental transition being here rather than there. He has to work through all the confusion and hurt he is feeling.
Good luck and keep to the high road.

i can relate. You have to continue to be his rock and committed parent. I transition my son back to me by asking questions that don't have yes/no answers. I try to lead him to that place of purging himself from the bull he was fed while he was there. Remember your son loves and needs you and he knows it.

I HAVE BEEN DIVORCED FOR 11 YRS FROM MY GIRLS DAD & 18 YRS FROM MY BOYS DAD. ITS NEVER EASY FOR A CHILD TO GO THROUGH THIS NO MATTER WHAT YOU DO. THEY GRIEVE THE LOSS OF THE OTHER PARENT & THE ONE THEY ARE WITH IS THE BAD GUY. IN THEIR EYES THE ABSENT PARENT IS THEIR HERO. DON'T TAKE IT PERSONALLY, ITS JUST HOW IT IS. WHEN THEY GET OLDER THEY WILL SEE THINGS FOR WHAT ITS WORTH & REALIZE THAT YOU WERE THEIR ROCK. IN THE MEANTIME NAME CALLING & MUDSLINGNING HAS TO ME OVERLOOKED. I TO WENT THROUGH A BAD DIVORCE AS A CHILD & I REFUSE TO PUT MY KIDS THROUGH THAT KIND OF ABUSE. AND YES IT IS ABUSE TO A CHILD WHEN YOUR USING THEM AS LEVERAGE AGAINST YOUR EX & TALKING BAD ABOUT THEM IN FRONT OF THE KIDS, OR PUMPING THEM FOR INFO. I HAVE ALWAYS STRIVED TO KEEP ON GOOD TERMS W/ THEIR DADS BECAUSE ITS JUST HEALTHIER FOR THEM IN EVERY WAY. WE DO THE HOLIDAYS, BIRTHDAYS & PRETTY MUCH EVERYTHING TOGETHER. WE EVEN HANG OUT TOGETHER FOR THE HECK OF IT. I KNOW THAT IN SOME SITUATIONS THIS ISN'T POSSIBLE & I AM FORTUNATE TO HAVE THIS W/ MY EX'S. IT TOOK ALOT ON MY PART TO SEE TO IT THAT MY KIDS HAD THIS IN THE BEGINNING. WE ALL SET DOWN & CAME UP W/ A PLAN TO HAVE PRETTY MUCH THE SAME RULES IN OUR HOUSE, SO THE MANIPULATING STOPPED. ALSO WE BACKED EACHOTHER ON DECISIONS IN THEIR BEST INTEREST. THEY STILL NEED TO ADJUST AFTER VISITS, BUT NOT AS BAD. ITS ALL A PROCESS. MAYBE IF YOU CAME UP W/ A TRADITION TO DO WHEN YOUR SON GETS HOME FROM HIS VISITS IT MIGHT HELP. LIKE BAKE COOKIES TOGETHER. YOU WILL BE ABLE TO REDIRECT ANY ILL FEELINGS/NEGATIVITY HE MAY HAVE, BE ABLE TO VISIT & LET HIM VENT IF HE NEEDS TO (W/O GETTING OFFENDED OR DOING WHAT THRIVER SAID) & THEN HAVE QUALITY TIME TOGETHER EATING YOUR WARM COOKIES W/ A GLASS OF MILK. MY EX IS TRYING TO TAKE MY 14 YR OLD NOW BECAUSE SHE WANTS TO LIVE W/ HIM TO FIX HIS DRUG/ALCOHOL PROBLEM. I WAS HURT & UPSET BUT I STILL LET HER VISIT BECAUSE HE IS HER DAD & I WILL NEVER TAKE THAT FROM HER.

I am glad I am not the only one with trouble during the transition. I know I need to stay on the high road. I know that eventually my son will realize that I am the one that has always been here for him. It is just sooo hard when he comes back from the visits that my ex and his gf bash me. I have to say that when my son visits only with his dad then I don't have near the problems. I don't want to point fingers, but that is what I have noticed. I have also been keeping a journal of how my son is behaving when he visits his dad and reading over it, it really does look like my son has more of a transition issue when the gf is around. I will keep the high road.