Advice needed for my significant other

My significant other is having issues with the mother of their one year old son. I try and not get involved as little as possible. As they have years of learning to deal with one another. He recently told her she needs to work and start paying her rent and cell phone. Last weekend he gave her his credit card and she spent 400 no questions asked for their son. Than came back and made a big deal bc she wants cash. He says she feels entitled. She also makes a big deal if she sees or hears he went out with me or with his friends. He’s a truck driver so his schedule is off. As Advise I told him to tell his job he can’t work every other weekend and give her consistency with see their son. Now she also has another child who the dad doesn’t give her anything and she comes down his throat for assistance with her as well. He’s frustrated any suggestions? I’m very mature about the situation bc she’s a woman like me so I always defend her as a woman. No she doesn’t like me I’ve been in his life for 8 months. As they didn’t get back together after their baby.