Don't do anything to mess with your boyfriend other than break up with him. I was with my last girlfriend for close to year. She dumped me through text messages in early april of last year.
Not only was she verbally abusive to me (criticized me a lot, made cruel jokes to me, yelled at me often over small things), was embarrassed to have me meet her family (I was kept a secret from her family), never said, "I love you to me at all" and manipulative (she kept secrets from me), she also went on a personals website while I was still her boyfriend. When I told her that I found out that I knew she had been going on the site, OkCupid, she said to me "What are you? Stalking me? She then told me she was going on there to just "fill out surveys." Not only did she go on that site, OkCupid to find another boyfriend, she kept in contact with her ex boyfriend before me who she claimed hurt her so much and made her so depressed that she turn to drinking and gained weight. She kept in contact with him through myspace and by talking to him over her phone. She went back to using Okcupid for a while after she dumped me through text messages. Your boyfriend has zero respect for himself and for you by going on personal sites. I should have broke up with my last girlfriend after finding out she had been going on OkCupid, for talking to her ex boyfriend and how badly she treated me most of the time, but I didn't. I broke up with her on three or four occasions but she wanted me to stay her boyfriend I guess to keep her company as she doesn't have a lot of real friends. She also used me until she found a better boyfriend that she would want to marry and have kids with. I get that you're angry and hurt but it's best to end the relationship you have with him. He doesn't care about you. You can never go back to trusting him again.
I hope that this helps and take care.