Am I over-reacting?

I am fed up with my other half. Baby was born 9 days ago, I've been home a week, and my mum left on Fri night. So we've basically been our new family unit for 2 days, including our 4yr old. While my mum was around, he let her take care of our daughter, cook meals, do chores etc whilst he spent most of his time on his computer gaming. Now she's gone, he suddenly 'doesn't feel very well', and spends the day huffing and sighing. Today, I was left alone in charge of both children for 6hrs while he stayed in bed and then got himself breakfast. In the afternoon, we went to the local park, but he decided he would be better off going home and cooking a pizza because he was hungry. So i was left on my own with them again. I'm thoroughly competent, so I don't necessarily NEED the help, but I feel like I deserve it, and that the children deserve a dad who wants to spend time with them and who makes them a priority. Our daughter couldn't sleep this evening, so I waited until baby was asleep, then put him down in the cot to go and settle her (over an hour past her normal bedtime). My partner was getting ready for an early night (to make up for all those coming to bed after midnight while my mum was here?), so was in the room with baby. After about 10mins baby is unsettled, but I am still trying to get daughter to sleep. Baby starts crying, and I hear OH trying to work out what night stop the crying. Within another 5mins, daughter is asleep, and I can go and take baby. But in that time I've heard partner tell the baby to both 'Shut up', and to 'Chill out for fuck's sake'. Obvs he's too young to take the words in atm, although the raised and frustrated vocal tone is probably something he can pick up on. Am I wrong to be bothered about this? It's his first real time 'alone' in charge of the baby, and he responds like this after 5mins crying. Is it just me finds that unacceptable?