Boyfriend’s mom is a psycho and now my parents too? Help!!!

Okay so here’s the deal, I’m 17 turning 18 in a couple of months and my boyfriend turned 17 last month. Our age gap is about 7 months apart and at the age of consent. (legal age gap is 4 years and age of consent is 16. This information will come in handy later, hold on) His mother doesn’t allow him to talk to girls even as friends so his whole family hid our relationship from her but one of his baby brothers slipped up after his grandparents took us and his little brothers to an amusement park to celebrate our 5 month anniversary and his grandma’s birthday. As far as most of his family knows we’ve been broken up since then but we’re going on our 11th month together and since he turned 17 he asked his mother about being in a relationship and they not only argued when he brought it up respectfully but she slapped him and he FaceTimed me while breaking down and crying with a hand print on his face. The only other time I saw him cry is when his great papa died within the first couple weeks of our relationship so it was obvious that argument and such had REALLY affected him. My parents know that we’re together but they won’t allow me to see him until we get permission from his mom, my mom wants to meet her and even get written consent of our relationship because my parents found out we’ve been sexually actively previously and don’t trust us to not do it again even though we’ve promised and they’re are afraid that if his mom finds out she’ll press charges and that I’ll have to register as a sex offender. Once again he’s 17 therefore over the age of consent, a perfectly reasonable age for a teen to be in a relationship, and she can’t pin it as being illegal because we’re far under the 4 year limit. What do I do?