Can I legally put a lock on my bedroom door ifI am getting a divorce?

Putting a lock on the door might be legal and might be something he can use against you in court. You can consider this person a trespasser and ask the person to leave. See if a police civil escort can come to the home and get this person to leave. The better route and one many lawyers in family court proceedings use is going to court, asking for restraining orders against the person coming into the home and even getting a restraining order or order to stay away for the other spouse. This is especially true if there are minor children living in the household or if there is domestic violence involved (present or a history thereof); the court will not look too kindly upon a person coming into the home when you two are still married. Keep in mind, some courts are also looking at the mistress (girlfriend) in cases of the spouse suing for the marriage ending.  Talk to a family lawyer in your state who is experienced with such matters and he or she can go through your better options than simply placing a lock on your bedroom door. Of course, if your are concerned about theft, you may wish to move your valuables to a safer location (family, banks, etc).