the origional agreement was also when you had one child. when dd was tiny we shared things that way too... then when i got preg with ds1 i insisted on some changes.
the way dp and i work it is if we're both in the house we're both responsible for everything, in the evenings dp does downstairs, all the dishes, cleaning up the days mess and sweeping/hoovering. meanwhile i deal with the kids and get them into bed... we used to alternate but he really hates doing the kids and tbh, i hate the cleaning so this works better
at the weekends it's the same, i tend to do more practical stuff as he's useless at anything laundry related but he in turn does way more for the kids... almost all poo incidents and deals with their incessant requests for juice/food/tv/toys... we both do a similar amount of random jobs like tidying up. i do all the cooking simply because he can't cook but i like cooking anyway so most of the time it doesn't bother me
while he's been gone for the longer day the last few weeks a fair few times he's come home to a demolished house.... he doesn't complain, in fact he tells me not to go mad trying to clean as he knows how hard it is and that the kids trash the place straight away again... as he says 'i get a lunch break and fag breaks.... the few times you get peaces from them you need to take a reak too, not kill yourself cleaning'
i'm in the extremely lucky position though of dp having been home with the kids by himself... when dd was 8 months i went to work PT and he stayed with her and freely admitted he found that hard enough and then obviously when aaron was born he had a week of dealing with all of this singlehandedly.... he knows what its like with the incessant demands and never getting a moments peace... like he says, at a job you're legally entitled to a certain amount of down time, as a parent you don't get that.
don't get me wrong, dp can be an absolute ass at times... our big issue here is sleep... why he's entitled to half day long lie ins no matter how long it's been since i've had one and there's also his typical male inability to see what needs doing but at least whatever his failings there's that recognition of what i do, that it's not easy being here with them some days, that there are days i'm in foul humour because i've been listening to dd and ds1 kill each other all day, that sometimes i just don't want to be touched becuase i've had children and babies in physical contact with me all day and i really need some breathing space.
but, the point i'm trying (very long windedly) to make is that all of these things had to be discussed, were fought about, screamed about, bags packed about and eventually over the space of 7 years together we've just about reached a point of agreement. you and you dp have been together a very short time in the grand scheme of things and you didn't get much time to get to know each other and learn to live together before having jacob.... it takes time, it take conversation, it takes compromise and even then there will be days where you want to rip his eyes out for no paticular reason... it doesn't mean ye can't work as a couple or that either of ye is even in the wrong... it's all part of sharing your life so closely with another person.