OK, everyone stop slagging this guy off - it's not constructive. OK, he said some very unreasonable things, but when you're stressed out and angry and your whole life has changed, you can act out (especially when you're anonymous). He's already said a ZILLION times that he's not really going to have an affair.
Chris, the problem here may be that you and your wife both had unrealistic expectations of how little your lives would change after the baby. Now she's realised how life-changing (and utterly exhausting) it is and you feel she's changed the goalposts.
I'm not surprised she's getting no housework done if she's up 5 times a night feeding the baby - she must be zombified with exhaustion - and this probably explains why she's feeling depressed and unsexy.
You've said yourself that you've probably been unsupportive and a bit of a prick, so don't say it to us, say it to her. Don't immediately swoop in with solutions - I've found childcare, I've organised a cleaner, etc - just sit down first and say sorry, that you know you haven't been supportive enough, that you love her very much and you're sorry that you weren't prepared enough for how overwhelming the changes in your life would be.
Then say that you want to help her and work with her so that you can both be happier. Sit down with her and discuss possible options and solutions - don't just tell her what you think should happen - and go through your household budget together so that you can work out what you need.
You'll probably find that after some tlc, some extra time off work and the regular services of a paid cleaner, she'll feel ready to contemplate part or full time return to work as the child gets older.
And the happier women are, the more cared for and appreciated they feel, the more sexy they feel.
You just need to think really carefully about what's most important to you: a happy, loving wife and a good relationship with your son, or a wealthy lifestyle?