I sacked in a very well paid job with a big plc as the 2 hour commute meant I saw too little of him (then his brother).
Set up on my own and had years of eating breakfast with them, popping home for lunch and eating our evening meal together/bath/bed (read 90% of the bedtime stories to our two for 10 years) and missed very few of their school stuff – concerts/sports/etc.
We took a big cash hit but prioritised the family above all else (hols in static caravan & tents, no new bikes or cars, dropping the need for expensive things/lifestyle).
Businesses are now running ok, still not flush but I have a brilliant relationship with my lads and (as far as I can judge) a good one with MrsCat too!
Sounds like your partner is doing a great job, perhaps a chat with her about how you feel once junior has gone to bed may open up some options.
But bear in mind, whatever you earn it cannot buy back the time that is passing now and they grow so much in the early years.