How do you keep going?

FTM to a lovely, 'easy' 3 month old. She only cries if she's overtired or hungry, sleeps through the night (for now and praying sleep regression doesn't come). This morning I didn't want to get up, she woke up at 7am. My husband fed her and put her back down in the cot and went to work.

I left her in there where she cooed, aahed for her whole wake window (about 1.5hrs or just shy) and then she fell asleep. I feel so guilty. I made myself some breakfast, a coffee and can't stop crying because I feel so guilty that I left her even though she wasn't crying and that I should have played with her or something. She's so wonderful but I don't feel like I'm a good mum because I don't want to be a one woman circus during her wake windows. Nobody warns you either that you spend half your life trying to get them to nap in the day. How does everyone do it? What do you do with your baby aside from tummy time or read to them even though your baby spends half it's time staring into the void? How do you get stuff done in the house? How do people want more kids? Before her I wanted two but if I don't enjoy being a mum now how could I ever want another? I still feel so guilty even though she didn't even cry once and fell asleep on her own.