just some ramblings...i'll probably come up with other nuggets as time goes on, but first and foremost
DO WHAT'S BEST FOR THE UNBORN CHILD!
if that someone is committed to their partner of 8 years, try like hell to make amends...there is a good chance it won't work out, but there is a small chance and it seems like that person is worth putting forth that effort.
talk to the pregnant person(i assume its a chick), and find out her intentions...does she want to be with you? is she willing to co-parent? sounds like she wants the baby and I would never suggest abortion(personally not an option for me).
through all this, make it as good as it can possibly be for this soon to be new born, they didn't choose to come into the world this way, but make it work for him/her, give him/her every possible option to grow up a happy person with tons of potential, no easy feat.
keep your head and wits about yourself...in the end this isn't a horrible thing...sure you may lose a lover, we all do. Sure there will be new responsibilities, personal, civil and financial, but we all deal with them, if the worst thing you will be facing is working harder to bring a productive child into the world, you are in pretty good shape.
DO WHAT'S BEST FOR THE UNBORN CHILD!
good luck and just know that you may lose some people around you, but most will stay and they will be invaluable in terms of being there as a support team...someday you will look back on this and realize that with the exception of a few weeks/months of heartache, everyone will come out on the other side better off.
DO WHAT'S BEST FOR THE UNBORN CHILD!