Well i had a talk with him about it and he agreed to stop doing that. When she realized he stopped telling her stuff about us she started to act weird with me. Like i would say hi to her and she would say hi and walk away and act really rude.
Think of what you're taking away from her. Do you expect her to act any differently?
And she started telling him things like u spend a lot of time with her, and ur cousin says he never sees u anymore or for example she told him he looked stressed out ever since he got with me. Well to make a long story short my boyfriend loves his mom alot and i feel like with me and her not being on good terms like we were makes things a lil awkward. Things were a lot easier when me and her got along. Any advice on what i can do to get back on her good side?
Seriously, you don't know what's causing the problem?
As for whether or not you're right to 'put up boundaries', I wouldn't go so far as to say either way. It's not a right or wrong issue, but a compatibility issue.
As an aside, if his mother is objective, she may actually provide him with good advice that can help your relationship with your boyfriend go smoother.