Shaz strange as this might sound, it was actually a bit of a relief to read a bit more from you in your post last night, in terms of your feelings about this. I think it's an indication that you have moved on a bit from the shock and are now processing some very human feelings of loss and sadness.
I wouldn't describe what you have done as "game-playing" either, it is simply taking control of a situation and taking back your power - not letting those two control your life and that of your son's without you having a say in it. I applaud what you have done - you did the right thing and won't regret it.
It does the situation no good whatsoever if your H thinks he can vacillate endlessly and keep his options open. I agree with posters who say that he is no doubt casting himself in the lead role of some "torn between two lovers" drama - and is getting an ego boost from that. Much better that he starts realising that his behaviour has caused him to be left with one (very dubious) woman, who doesn't seem to be certain about him herself - and without the woman he vowed to love and daily contact with the child he professes to adore.
I'm sure others are right that the OW might feel very differently when reality kicks in and she has to deal with others' reactions to her role in breaking up a young father's marriage - and a toddler with sticky fingers in her child-free house will prove to be an effective passion-killer. However, yet again I imagine you don't want her to be the reason he sees sense, do you?
If he does ever get his head out of his arse long enough to conclude that she isn't what he wants, then of course it will be your call to decide if you can forgive. But (and this is entirely personal, because I know I could never have done it) it's a different matter forgiving if he only comes back because he was dumped by the OW.
In your situation, if he ever does decide it is you he wants, I'd be doing a lot of checking behind the scenes and talking to the OW, if necessary, to establish the truth.