I'm separating but I was in a stable union, what now?

If you were in a stable union with this person, you have the same rights as if you were married - married under the partial community of property regime. So, ideally, you should go to a lawyer so that you can get a divorce. And then the judge in that divorce will decree what you are entitled to. You'll even have to ask for maintenance, maintenance for your son. Since he's a minor, a judge, together with the Public Prosecutor's Office, will decide how much alimony needs to be paid. So, in this case, you need to seek recognition of the stable union and dissolution after the divorce.