This is why I chose to do my masters research in the area. Make it clear that it's over. Let's change the culture from the all-or-nothing face-to-face or disappearing act to make space for the means in-between. I don't think there's anything at all unusual about dating multiple people, in fact I think it's downright common and completely to be expected. Saying that you don't think you're right for him is basically a nicer and still valid way of saying you don't think he's right for you.
And, odds are, if he's not the right fit for you, you're also not the right fit for him.
12 Nice Ways To Break Up With The Guy You're Kinda Dating
Thanks for letting us know. Do It. Consciously or not, you are leading them on. Don't keep sleeping with them if you know they want more. Or if this is all too much, you can always run away screaming and waving your arms: If it were me, I'd think to myself "OK, I'll be patient and let her find out what I'm like, and hopefully she'll wind up wanting to date me exclusively. At the end of it all, it sucks for both parties.