Argument with SO

So today me and my SO got into a stupid argument and we don't argue a ton but when we do it seems to be a cycle of him moving to extremes. Like, he'll say, you drive me to drink even though any other time he'll say he drinks beer because of stress from work. Or because he pays the rent he'll throw it in my face and say this is his house only during a fight. Mind you everything in this house is mine and I never think about that until he throws it in my face about how HE pays the rent. We have one child together and I am 6 months pregnant currently with our second child which makes this that much more complicated. The argument today he also stated how awful I am etc but never acts like that any other time or says anything mean like that when we aren't arguing. Should I take his words during these arguments seriously since it seems to be a pattern? Also, how do I get him to stop looking at things as mine and his instead of ours? I look at this house as ours and we both contribute. I want to get to a place where we are sharing finances but he is still so separate when it comes to that. After a 3 year old and one on the way I really want to move forward and combine all aspects of our life. How can I get him to see these things and stop the yours/mine mentality?