My partner,of 7 years,& myself are not getting on?

The problem is my partner has a problem mother,She has a lot of health problems and she has been told by her doctor not to go any holidays until tests are done on her as she had what we think was a mini stroke.She's getting very abusive and forgetful and what is she doing this coming week,she's coming up from Lancaster,England to Glasgow,Scotland in the coach with a zimmer frame as she's also not too good on her feet.She's met a man 20 years younger than her "a toyboy",he's is no a very nice man at all as all he's doing is using her.She pays for everything they do together as he's got no job but he's running her dry of money,WE had a day out with them last year,my partner & I,we went to Largs,Ayrshire,and he went mad,he stripped off all his clothes and I saw it all and he wet into the sea right next to the ferry,he could have been killed,then on the way back,we had a big argument and they put us out of the car,we had to get the train back.I was very angry and all my partner could say was it was all my fault(which it wasn't),as the so called "boyfriend" he got very abusive and my partners mother punched me in the back to get me out of the car.I have threatened to leave my partner,which would devastate er but what do I do,I cant speak to my partner as she blames me and I don't want anything to do with her mother.She's even had words with her doctor,so at the moment she doesn't have any care,which she needs.Then shes coming back to Scotland in June for her granddaughters wedding.I just want to run away from the whole lot of them.