Just found this on the mass.gov site when I was double checking some info… “Who has child custody before going to court? If the parents aren't married — The mother has sole legal and physical custody of her child until a court orders otherwise.”

So if it were me, I’d stay in the UK, lock down a job ASAP assuming your family is able to help with child care, consult with a MA family law attorney asap, consult with a UK attorney asap, and begin preparing the forms yourself to file for full custody of your child and a probably a restraining order against the child’s father for the abuse. You will have to file an affidavit documenting the abuse so be as specific and direct as possible. The MA Probate & Family Court site has the forms available as well as links to each county’s remote/virtual court services so you can speak with court personnel face-to-face about the correct steps without having to leave the UK. Please know that it’s not an easy process but it’ll be completely worth it to keep you and your child safe and supported.