Regaining trust after unfaithfulness

My partner was sexting a girl about 2 years ago until i caught him. Then he randomly got a messgage from a girl who he used to sleep with and it was very flirty ... he lied about who she was until he knew i knew all about it.

It got to the point he stopped watching porn and hasnt really talked to ANY girls in the past 12 months.

Heres the thing... i am having trouble trusting him now to a point i always feel the need to snoop "in case" .... its doing my head in. What do i do? I know snooping is wrong but i dont wanna be fucked over again