I know exactly what you mean. the hard thing is stopping yourself from thinking about him and what he is doing with whom and how great it potentially is. You need to focus on you and what you are doing to make yourself happy. Change what you can. I know easier said than done, but with practice you can.
perhaps it is a lesson with respect to the poem about serenity and wisdom... or a lesson in behavioural therapy.. train yourself to focus on you! not him!
good luck... i am in a similar boat and am trying to do the same.
