My boyfriend still a member of internet dating site. What should I do?

Just found out my boyfriend of 1 year still belong to this internet dating site where we met. At first, I found out that he updated his profile, so I asked him why. He said he doesn't know. Just want to do it. I asked him specifically if he is looking for another. His answer no. So I was ok with that. I thought as long as he doesn't looking or answer any email that he received, it's ok with me. But then about 3 weeks ago, I found out he is been emailing a woman from the same internet dating site. Do you want to know how I found out? He mistakenly sent that email to me! Go figure. So I confronted him again. He said he was sorry, and again told me that I am the only one he loves. He was just looking for friends. All kind of stuff. He said he was just taking his friends suggestion to test me, whether I am a controlling partner or not. I know all of you would say just take off and move on. Although it's only a year , we have been through and invest a lot in this relationship. I don't know it is the right thing to do to throw that away. HELP!