Help w/ my relationship

Me and my boyfriend got into this argument due to me finding the old dating website he has to have although it was old it got me bother. Later in the argument he had admitted to me he was on it 4 months ago a while back into our relation and we been together for 8 months.. & honestly it hurts bc he said he did it bc we weren’t as serious & things weren’t the best but neither the WORST times we just had our times & he had said he got it but never actually meet anyone & had it for two days he did talk to some girls & at times talked dirty as well.. & even though he was honest it hurts bc I wanna trust him and idk if I should leave him bc for me that’s cheating .. he was arranging other dates to fuck even tho he wasn’t going to do it but it hurts to think at the fact that he did that behind my back and him keeping this for the longest.. I personally in my relation have made mistakes but never have I hide things .. I always talk to him right away as much as it puts our relationship at risk. Any advice ?