gf excludes my son

My girlfriend and I have been together for a few years and we have been trying for a baby...
A while ago, we broke up for a bit and I slept with another girl (Ayriah) she fell pregnant and I have a 1 year old son with her...
We share 50/50 custody, we have a week each then he goes to the other.. we didn't go through the court we just decided that this would be best for our son and we allow the other to call in during the time the other has him, if needed..
I'm starting to notice that my girlfriend excludes my son from things.. 
For example we had a party, my friends and her family brought their kids over and she completely ignored my son the whole time, she also refuses to play with him, she complains that he's too loud when she's watching tv, she says that I cuddle with him too much and when I try talk to her about it she mocks me and says I'm too serious and then talks shit about Ayriah saying how she's a terrible mother, a bitch, that she's disgusting with all her tattoos (which is completely not true, she's the best mother)
What am I meant to do? Will she ever change? Will it get worse? I get maybe it hurts that I had a child with someone but we were broken up, it was an accident but I love my son more than anything in this world, being a father is the best feeling in the world and I'd never take that one night stand back because it brought me the most amazing thing in the world..
Am I over reacting? Should I try make it work? Should I just end it?
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UPDATE: broke up today because she slapped my sons face because he kept leaving his toys on the floor instead of "putting them away"
Thanks for the words ladies.