"I had absolutely no idea he was unhappy."
Of course you didn't, because he wasn't. He is rewriting history before your very eyes, because otherwise he'd have to say that he's been an idiot, an unfaithful idiot, and he can't admit to that - not to you, and probably not to himself either.
Anyway, forget him for the moment - what do YOU want?
Because if you DO want to save your marriage, you really are looking at chucking him out. ^"He can’t make a decision apparently" - well he doesn't have to as it stands, does he? He's got you standing patiently by, awaiting his wordsIndeed, standing patiently by and still having sex with him. It must be very tempting to just keep it going as long as possible - the sensation of power, the feeling of being in control of the fate of others. Quite intoxicating, I imagine. Well, you have to put a stop to that fuckery, don't you? Because if you don't, your marriage is truly over.
He needs to be brought back into touch with reality. He needs to know what he has put at risk. Right now he doesn't, because he has lost NOTHING. So, take the control over you away from him, and back into your own hands. Tell him that you have decided it is time to call it a day, he has to move out ASAP. He can move to his family, his friends, his colleague/shag, a bedsit on his own, anywhere he pleases but your home is no longer his home and he needs to pack up and leave.
Only then will he stop pretending to himself that he is the tortured hero of some melodramatic balderdashTV movie, and get his arse into gear. And whilst he lives elsewhere, you will have the headspace to consider what you want in your future. It might be him, it might not. But you won't know until you've had some space to yourself to think, to consider, to decide. Best of luck.