cheating family?

my husbands dad cheated on his mom, she found out and cheated on him back. apparently she got pregnant by the dude she cheated w and his dad divorced her. now, thruout my years w my husband, ive always known that his ex wife cheated on him multiple times w 4 guys. and hes always been faithful, only had eyes for her. her friends said she never cheated, but his fam said she did. she finally left him w the 4th one, they have kids now. anyways, i just found out that he cheated on her multiple times too, begging her friend for sex while she was pregnant and had sex w multiple women while stationed in s.korea. he was never faithful to her nor have eyes for her only like how he stated. idk what i have gotten myself into, i feel like what makes me think he wont cheat on me too when he cheated on his ex? what to do?