I caught him role-playing online...but as a female

Mary

so me and my boyfriend of 4 years recently moved in together, and he hasn't been as "excited" with me. I personally thought it was just because of stress or something...but it's been getting worse, well I know I shouldn't have but I went snooping, and I found a tablet, I went peeking around and I found an email, a female based email, that was having sexual role play with guys...now I don't know what to do or how to handle this, and I know he is the one playing it because of the way the sentences are written...any suggestions?