hi FAB
it's hard when you can't help thinking obsessivly about something that cannot be resolved ... i had this last year ... i think it's a process of acceptance that you will have to work out with yourself and with the more existential stuff it can be really tough ... but you will get there...
some practical advice ... try chamomile tea to relax yourself if you are tense and i found that abstract puzzles such as suduko and solitaire were good for cutting off neurotic obsessive thinking.
and remember we are all pretty wierd if you think about it so i'll bet that lot's of people will have had the similar thoughts and worries as you ....you're not alone in this ...
take care love