Husband has extramarital affair, treats me badly & mentally tortures

Sir I'm married from last 10 years n have one son 8 year.from last 3 years my husband was in extramarital relation with to b divorced lady works in same company.i came to know abt this in mar2016 so he was denying but our son was with him once he visited to resort with lady so son witnessed n told me this woman.he many times hit me n given shit words n for 6 months he was sleeping in hall not with me.many times wen w argue he tells he is in relation just bcoz of son else he wud have thrown me.now a days that lady started in our nearest area n he used to go to same office wen I cam to know I done nc against husband n lady saying I hav threat from both n same day women cell i complained but after that he send me notice n 10 pages all against me n my behaviour.i have not replied neither received but in women cell he given in written he won't b in contact bto that lady days he received call from her from office number.i think he is waiting for my son to b 10 yrs.do he get custody.