Definitely stop giving a rat's ass about her ex no matter how much he provokes her. Be totally indifferent and not care about anything he does no matter how blood-curling. The more she engages with what he does, the more he likes it and gets off of it. Truly it takes passion to HATE someone which we see with Tae Oh - still completely in love with his wife to the point of maniac obsession. So Sun Woo - disengage. Move if you have to. South Korea is a big place. You will not lose anything - 99.9% of the people in Gosan are shit to you anyway. No one is a real friend. What will you lose? ALL THAT BAGGAGE. So start anew, friend.

Really you have divorced him, and got your son. Take a break, relax, move away from the neighborhood. Go to therapy with your son. And when you are comfortable, find someone new. 

Your son already told you why he doesn't feel connected to you, improve on that. Even though you divorced your husband, he is still his child. Regardless of his present feelings, he will remain attached to the father regardless. So let him meet when he wants to meet.