dont worry mate, it will all be a memory in the distant past one day. I am 10 years down the track from similar circumstances, separated after 15 years, 3 kids 15, 13 and 9. looking back i had some of the best times ever, with just me and the kids over that time. As Mrs Swordie said, they do make their own choices one day, just keep being a good dad and you cant go wrong.
i had some great fishing trips on my weekends as well, its cheap, memorable, and the kids cant wait for next time.
one day you will wake up and everything will be sitting just right in your world and dont worry it sneaks up on you without notice, better times are just ahead.
cheers,
Kev