don't sleep with him anymore. he may have caught性病and u don't want to have another kid with him...one more person to suffer.
Clearly, he lef u just when u needed him most, during 坐月. Neither you nor your son is important to him.
Just live under the same roof and use him as ATM.
If he really promises to change, ask him to come back to HK and let you see all his messages, no private phone calls after work. come home after work every night. Probation for 1 year. If he cannot do it, he can not be trusted again. Just live with Mr. ATM until you can get a job. He has to pay you and your son an allowance even if you divorce.