Sex after an affair

My husband recently attempted to cheat on me (he tried to make a move on another woman but she stopped it). We are trying to work things out, but how do i know when its ok to have sex with him again? He wants to but im not sure if i do. I have no idea if there have been others that he has actually cheated with. He says there is not, but obviously im having a hard time trusting him. Has anyone experienced something like this that can offer some advice/support? PLEASE!

NOTE: i have been tested for STDs and everything is good