Sticking to your guns is the right move.
I don’t think it really matters what his motives are when the relationship has already gone the way of all flesh – as has already been said.
If you’re dead certain that he was playing the field, then really you shouldn’t even be questioning what his motives are, because let’s face it, why would you risk even contemplating going back to the guy – which you’re not, right?
Relationships screw up for so many possible reasons, if you guys got distant then it’s one of two possibilities there, you either weren’t great in the communications department – so that won’t have helped any to begin with – or he was up to no good. Now, if you had proof then it’s fair to say you’re in the right and he’s in the wrong and you should let sleeping dogs (or dogs that sleep around) lie.
Now here’s where I have a problem beyond this point. You mention that in your e-mail you basically accused him of cheating. Now, I don’t know how many guys I can speak for on this subject, but having been accused – falsely I might add – more than once by at least one person of cheating on them – I get not only hurt by it, but it also really pisses me the heck right off annoys me. If someone is going to accuse me of that, they need something more than just a hunch or a whim, and on every occasion it’s been just a hunch or a whim.
Logically though, if I was him, I’d still be really pissed off at you for accusing me of cheating and I’d probably actually reply to the e-mail….but what gets me thinking he was playing the field in the first place is that he is now texting you. So I get the impression that others are getting in that he was playing the field. Now I’m terrible at being the judge of anyone, it doesn’t suit me well at all, mostly because I dislike it, but, I think you need to just leave this one well alone and disregard any thoughts you have about this matter. Move swiftly onward.