cheat and sex

What is your advice when you partner cheats just for sex without moving to an affair but also without breaking up with you?
I figured he has somelike sex addiction in cheating not with one person but with 2-3 and at the same time he says the sex is not interest with me anymore. How cAn that be when having sex with others i wonder...
We had break up before because things werent getting honest but he always comes. Back and begging and i fall.. i have lost my trust but i have invest a lot in this relationship and i dont know what to do anymore
Ps all these he  doent know that i know i havent tell him yet because if i tell i will definitely break up forever and im not sure im ready for that.. we truly love each other