I definitely understand where you are at. We told our kids two weeks ago. I always thought that it would be easier if the kids were older but that is not true. My two oldest kids are grown and, to be honest, have been the hardest. They have not known any other life but their parents married...happy or not. My 13 year old boy is handling things as well I would expect.
I feel the same about feeling guilty about tearing my family apart. My STBX and I have actually been very amicable. He is still living in the house but is looking for a place. I know I cannot live in this marriage...even after much doubting...I know it is the right decision. Many women on here have given me good feedback so you are in the right place for support.
Good luck! Kids are a challenge but no matter what they are the most precious gift. They will always treat mom the worst because we always love them and accept them no matter what.