I think my husband is cheating on me with his coworker

I know the password of all social media of my husband, so recently I check up his facebook and he was talking to a coworker, actually they were flirting. Well I didn’t ask him anything, the other day I get in his messenger he already delete the conversation and when I asked him, he told me that he delete the conversation because his supervisor get into his phone and that’s why he delete it. I don’t really believe him. What should I do?

Btw in the past he cheated me🙄