I'm going to end my long term friendship because of his girlfriend
Is there something going on between you and the girlfriend?
Yes, I feel she's getting in the way of us and to top it all she thinks I'm corrupting her boyfriend.
New relationships will without a doubt change the dynamic of old friendships, but its important to know that this is natural. While you may not get along with your friends girlfriend, that does not mean that you have to break off your friendship. Instead, try to just treat the girlfriend as nicely as you can, and if she doesnt like you then at least you can say that you are trying your best for your friend.
Being nice to her doesn't change the fact that she is getting in the way of having a good relationship between me and my friend.
Nonetheless, cutting off your friend because you don't get along with his gf is not correct. Throwing away a long term relationship with your friend would be a real waste and it would hurt everyone involved.