Chris if you are still reading, I think my OH would have had fleeting thoughts not disimilar to your own when we first had dc (although I think he would have- and did- challenge himself pretty quickly about how reasonable or otherwise they were). I know for a fact he had expectations about what the house would look like when I was 'off work all the time' on maternity leave, and really struggled to see why, when dc couldn't actually move anywhere, the house would still look like a bombsite on his return from work some days...
If she's still being woken 5 or 6 times a night she will be doing her nut, to put it bluntly, and that level of sleep deprivation alone will make her emotional, shattered and leave very little energy for much else. It's the sleep deprivation, not breastfeeding, that'll be impacting on her.
How much support does your wife have? Other mums, going out to groups etc..? Does she have people she can talk over the night feeds/ BLW with? Do you? It sounds like you're both feeling a bit helpless with it all.
Life has changed MASSIVELY and the best way forward is to try and embrace it. Your previous lifestyle has gone anyway I'm afraid, even with the same amount of income the quirky bistros, deluxe hotels (or whatever it is you want to hold on to) are irrevocably going to be different now a baby is here.
I did go back to work (after almost 12 months)- I think someone on here suggested your wife poss extended maternity leave until then? A good suggestion which would give you both some time. I can see how, being practical and wanting to help my OH might have done something similar and found a great nursery, unfortunately I would have been bloody furious and really upset if he had- irrational as it might seem!
I think it's fairly common for sex to go out of the window for a bit- talking about an affair sounds a bit like you're trying to threaten your wife/ show her you have needs too etc...- but if you love her and you want your marriage to continue then it's a stupid thing to do that you'll regret.
Also what's your relationship with your son? You sound a bit disconnected from him to be honest. Can you start spending more time with him, both to give her a break, but also to feel more of a family? Maybe then you'll see more where she's coming from in terms of a reduction in income but an increase in quality of life?