Hi M.... How about calling a lawyer? You're going to need one anyway. You will need on that knows the law - I fear for you looking for advice from people that don't know it.
Otherwise - regarding starting over. Your whole life right now should be focused on your child. FORGET DATING!!! (Unless that was a joke, which maybe it was.)
The very last thing your son needs in his life right now is another man! There are so many negative implications of this right now - for him and for you.
Your marriage and dreams are ending. You need time to grieve and mourn - that can't be rushed. And just try for a moment to feel what your son must be feeling - his dad has disappeared!! He has NO IDEA why, nor is "why" a question. There's just a gaping hole in his life and he's now living with strangers. (Not strangers to you, but strangers to him. Strange sounds, strange smells, strange faces... and where's Daddy's face?)
Get it?
So my other very strong suggestion is to run, not walk, to a very good therapist's office so you can be sure to do your best to support your son through this difficult and traumatic time.
Difficult and traumatic for you as well. But you must live in it and walk through it. There is no shortcut or quick fix. Feel the pain. Live in the loneliness. There's a gift in all of it and you will be stronger and better as a result.
So walk through the fire - look for the gift. Don't focus on the negative. Be your own strong, mature person with a good parenting relationship with your ex-husband before you bring a new man into your son's life.
It's worth it - just for him.
Blessings to you. Be strong. Cry a lot if you have to.
This is just a season in your life. It will pass.