my husband cheated me.....?

[Help]

i m a married Muslim women having two kids,i had the love marriage it has been now 5 years pass,i got to know on 1st year of my marriage that my husband have a intense friendship with my sister (they talk also before my marriage),they usually talk on phone,sms and on net,i told this to my family,the situation get critical then i forgive him and save my marriage and i dont want to spoil the child future then after few days of my 2nd kid birthday,i get to knew that my husband cut his hand(he also did it for me b4 the marriage) for my sister and send the pictures on her mail account(he already block him),we fight alot and i told him i want to leave you,he also make harsh attitude and said i will not leave you otherwise i will take the kids,he dont have any other bad habbit nor he have any physical relation with other gals,now the few days before i get to know that he having call on my sister account of around 15 min,9 min,2 min by voice calling software over the internet ,my sis deny he said i dont talk,she said i have the proof i was with mum,she is not accepting,she said i dont have any contact with him nor she want...he have the lock on his mobile,when i argue with him he said i will do it,if you want to leave then leave but i will not give you kids,and i make friendship on social media as well i will do 2nd marriage,every time he said this thing just to threaten me or he have the plans i dont know?situation gets so worst.i dont understand what to do?leave him or stay with him like a stranger just for the sake of kids?right now i said him dont talk with me and have any relation with me i am here in this home just for the sake of these two boys.one is 3 and a half and one is 2 years old....please guide me and tell me what to do?