Extra marital Affair, Domestic violence,divorce, maintenance

Dear Sir, Married in 2008. I am frm hyd...my husband family in Hyderabad..he used to work in pune..i used to stay with in laws as i was working n used my money for every household expense( i am a post graduate n used to wok in IT company with 5 digit salary)...did not take me to pune..mil tortured to core was treated like house maid, fil used to abuse ...found out extra marital affair of my husband with a muslim girl all this within 1 yr of marriage..wanted to get out of it ...my husband pleaded n fell on my feet to give him a chance to prove himself ... i gave him second chance as my parents especially my father was fighting with cancer at that point of time..did not disclose anything abt him to any one... Shifted me to pune searched for my job in pune...but still in pune also entire house expenses were borne frm my salary...he used to support me in front of his family n his parents ...i have a son n from the time i delivered, since i had no support to look after my baby i had quit my job...since than he had cut down physical n emotional relation with me..his behaviour changed...it was always a mental torture n verbal abuse n criticisim ...he bough the girl with whom he had affair n recommended job in his team ...hoildays, festivals, week days , weekends he is always in office frm morning till midight, gave away car to her, removed servant maid help for me, not even a single minute they dont end chatting either in sms or company emails or phone calls...he completely ignored me n my son....does not give money for house expenses, bought a new house on his name..started treating me like a slave...if i ask money for house expenses he creates a scene that iam money minded ..he calls his parents n says iam thief ... unable to bear more of it i took my son, n jewellery given by my parents during marriage n left to my parents house...its 1 year now...i am looking for job not anything concrete yet as i had a gap of 2yrs...he is threatening me that if i file a divorce case or ask money for maintenance he will take away my son... no body frm my in-laws contacted me after i told what he was doing to me n his extra marital affair...i cld find that he had another 2-3 affairs earlier to this as well... now he shifted to the new house which he purchased , his parents n sister -in-laws all staying n living happily... recently had got sms that if i will not let my son be with him it will be a curse , i hv spoiled my life leaving the house, he just want his son to live luxury life, i can stay under one roof separate for my son, and i will not get anything after his death ... pls guide me what i need to do... my son is now 3 complete and 4th year running no evidences for verbal abuses n mental torture he confessedd in frmont of me of his extra marital affair but no relevant evidences how shld i teach such people a lesson ?