Can my boyfriend sing the birth certificate even though I’m still married

In general, signing the birth certificate as the father is an acknowledgment of paternity. However, different jurisdictions have different rules on this matter. For example, in many jurisdictions, if a woman is married but separated from her husband, and she becomes pregnant by another man, the law may still recognize her husband as the legal father of the child. This is the "presumption of paternity" principle, which holds that a woman's husband is the presumed father of any children born during the marriage. It can make things legally complex when the biological father is someone else. The situation you described is a complex legal issue that could involve both family law (concerning divorce and child custody matters) and paternity law. Disestablishing the presumption of paternity and having the biological father recognized legally could involve a court proceeding and may require DNA tests. To get the most accurate advice for your specific situation, you should reach out to a legal professional who is well-versed in family and paternity law in your jurisdiction. Understanding the specifics of your situation would enable an Anne Arundel County divorce lawyer, or a competent attorney from your jurisdiction, to advise you on the best course of action to take in this case.