No need to apologise for the way you are feeling Jonny, that's what mates are here for.
I don't feel I can give you much advice because it is something you have to work out for yourself IMO. But certainly use us as a sounding board for your thoughts and frustrations.
The only thing I can do is to remind you that you didn't marry K's family, you married her, leave them out of it as much as possible and you may have some foundations for working stuff out.
Not much help I know but what do I know? You are two lovely people and six months is not that long really, sit and talk to each other, if your not shouting you might be heard and you may hear her too!
Over to the other more life experienced forces of our forum...........