Assalamualaikum warahmataullahi wabarakatuh
Cheating in Marriage is the worst case among all the disputes occur between husband and wife, Islam prohibits it for both man and women, but if you found your husband cheating on you, kindly consider the following steps:
1- Make sure 100 % that he is cheating, do not decide it just by some signs or habit. May be he is not like what you are thinking,

2- if you find him a cheater, have a clear discussion with him before anyone , because do not let any one enter your relation unless it goes so far, and if he accepts to leave Haram relationships, forgive him and live a happy life.

3- if he continues to have haram relations , add some one from your family who you think the most suitable person to handle the situation and let him try to convince him.

4- if all the above options fail, ask him to leave you. Allah will grant you someone better than him

JazakALLAH o khaira