I wouldn't consider what he is doing 'cheating' but it is definitely a very wrong move on his part. Its a huge breach of trust. No, it is nothing compared to 'seeing other girls on the street' because his profile shows him as an interested party seeking someone else, not an anonymous browser of profiles.
The fact that he told you (I'm assuming this was just out of the blue he told you, not that it came out during an argument or you saw him browsing on his pc) shows he does not consider the consequences of his actions... OR... he is using this as a means to manipulate you...kind of like to make you feel like you have to compete to keep him.
The 'keeping his options open' part is perhaps the most hurtful and asshat move of the whole thing.
Personally, I'd say dump him already. With that last comment he has already stated he is ready to move on, perhaps as soon as he gets a positive on those dating sites.
edit: I've read your previous posts.. in which I replied back then as well. Seeing all of the issues you have with him I'm inclined to believe that you're basically becoming his second mother, not a life partner. I can see you love him but take a step back and see objectively what kind of future you would have with this person.. both financially and emotionally. From the little glimpse you've given in your posts I don't see it as a positive one. Its your life, do what is best for you not for him.