Either get married OR both of you go to a solicitor and tie up all the legal threads.
What worries me is how many people simply don't know that "common law spouse" is NOT a legal status equivilant to spouse.
I only got married because my brother walked out on my SIL and their child when she was 8 months pregnant with their second child. Neither she nor I were prepared for what the solicitor told her when the fact they lived together was put on the table.
To be honest I chose marriage cos it is a one time deal with rights that cannot be taken away behind my back. Even if SIL and Ex Brother had done all the legals I'm 100% sure he would have changed all the paperwork, like wills, insurance etc behind her back. Not that he needed to really, considering that he was free to marry immdediatly, which is what he did, thus confering rights on OW that would have cut SIL out of the loop anyway.
I am with DH becuase I want to be, not cos we are married. I was married before and a peice of paper is not a ball and chain when things go so bent that being together is pain rather than pleasure.
Divorce is a pain in the bum, especially if you and your husband are from different countries and you are trying to sort out a divorce in a thrid country. Still a million ti es better than what SIL went through.
I love and trust my husband, but then I loved and trusted my brother.. for my son's sake and my sake I want to aviod an additional practical nightmare just when emotional pain is taking all my attention should DH inexplicably have a personality translaplant and turn into a right lying, cheating, duplicious, moral free bastard.
I know lots of people who live together happily, but it was the handful who didn't get a happy ending that swayed me. But then I am a very glass half empty person, in the sense I have a hard time believing that I am somehow immune from becoming one of the very unlucky ones who got blindsided by behavior they in no way could have predicted.