UGH...he loves the OW??? I don't think S4 means this in its true sense. She is probably nice to him and spoils him. I know you hate all this but at least you know that the boys are not miserable when they are with their father.
If OW is not supposed to watch the kids and they were left alone with her contact your L...he is in contempt of court!!! When H and I started dating his xw prohibited him to let the kids be around me...they were already D'd...I was not OW and she still enforced it, this got to the point (over 2 years before I met my stepsons!) that they had to go to court and the judge ordered her to let me meet the kids unless she felt I was a danger to them. I guess the difference between me and the OW's out there is that I respected her wishes and would only see H when the boys were not around...Once I did meet the kids there were still NO overnights. They did not see us in the same bed until we got married!! We lived together and H would sleep on the couch when we had the boys.
Sooo my point is you have a very strong voice being a mom...you can push and push for as many rights as you can!!