My husband and I are thinking about a temporary separation to sort our relationship out.

Abandonment is not the big issue that it used to be in MD. There are much larger issues for the Court to consider when deciding issues of property distribution and/or custody. Before you move out, consult with an attorney. If you have moved out, go consult with an attorney anyway. Your may be wise to have some Agreement in writing that you are "sharing" custody, however, that too has VERY SERIOUS implications later on in your divorce/custody. Really, what you are doing now can cost your thousands of dollars and many tears down the road. Please go see an Attorney about what your rights are, and what the effects of your decision will be in the immediate future. FYI: there is no such thing as a "temporary separation". You have been warned.

If the separation is voluntary, then it is not abandonment. I strongly recommend that you and you husband put in place an agreement regarding custody and visitation and confirming that your leaving the home cannot be used against you in the future.
You would be well advised to speak with a lawyer before you take any actions.

I strongly suggest an agreement in writing that you will share time with your son and you leaving the marital home is a mutual decision and cannot be used against you. The court would not consider you leaving abandonment unless you left with no further ties, no support, etc. You also need to determine how the bills will be paid for the home and who will pay them. This should also be in writing.