I recently got a RO on my ex for harassing phone calls and emails. When he calls, tell him to stop calling and do not engage him. Keep any messages (especially threatening ones). Make a harassment report at your police department. Do not allow your new husband to have words with him, simply allow him to bury himself and document everything!

However, if he is not abusing your son, I don't know that you have a case. Do you believe your son is in immediate danger? If so, get the RO.