His mother is so intrusive!

My boyfriend's mother has been so intrusive. He's 22, I'm 25. We have our own apartment, pay our own bills etc. He has yet to change his legal address (even though I have asked him to multiple times since this has been a problem in the past) so his mail still goes to his parent's house. Yesterday his mom opened his mail and found out he co-signed on my vehicle and she freaked out about it. He does not pay for my car or for the insurance or for anything for me. We each pay half on the bills for living and pay for our own vehicles, phones, etc. and I tend to buy him/pay for more things being as I make a little more than he does. He only used his credit to help me out. I'm so frustrated with this because I feel like we're in an adult relationship, trying for a baby, and he's still being parented as if he's 16. And on top of that, when she found out, she texted him and his phone went off, I asked what it was about and he lied because he "didn't want to hurt my feelings". Am I wrong to feel hurt that she thinks I'm using him and he lied to me about it to "prevent a fight"?