Under the circumstances you should file for sole custody. See if she dodges that summons... If she can't be served, you will be granted sole custody. I've never seen a case where that didn't happen when the other parent failed to be able to be served or show up for court. The Judge would most likely continue it the first time in another attempt to serve her and preserve her interests but if she still can't be served, you will get what you are asking for by default.
If you can make it on your own financially, you should probably count on having to do so indefinitely.
I'm sorry for the situation.
Your son is lucky he has you.
Hang in there.
"Let anyone who thinks he stands take heed lest he fall" 1 Cor. 10:12