The writer is comparing the activity of dating to a sport of some kind, where one can win medals (as in the Olympics, for instance). The word 'stakes' refers to betting - usually on horse races - and the higher the stakes (the amount of money betted), the higher the risks. The writer is therefore combining imagery from sport and betting and transferring it to dating, which he obviously sees as a kind of game or sport which people either win or lose. 'waste her heart': one usually talks about wasting energy or effort on something, or wasting some kind of resource, like water or electricity. Here the writer is seeing the human heart as some kind of energy system or resource, for example, that can be 'wasted', and what he is really asking is why the person he is referring to should waste her TIME dating 'some Swedish aristo-brat' (which is a word play on 'aristocrat'). He is transferring the image of a resource that can be wasted to the human heart, in other words.