To marry you need to find a girl (or a guy) and give them gifts and use charming expressions - the middle finger doesn't seem to get them going, sadly...
Once they have a gold heart above their head the option to marry will come up - but if you don't have a house, they'll tell you they can't marry you. Plus you need a ring which can be bought from traders.
To buy a house, (there is one in every town available to buy) then select the for sale sign and purchase it. To upgrade the furnishings, go back to the sign and you'll have the option to upgrade three times in total, I think
Then get married, have sex and kill her
Quest related stuff I am so rusty on, so someone else will have to tell you that...