Guilt can be a very powerful force. Some attorneys will trudge into the same firm or company day-in and day-out knowing that it is not where they want to be – just to avoid the guilt of leaving.
You have applied for jobs, interviewed and finally came through with an offer on a position that truly excites you and the only is thing in your way at this point is giving notice. For some people this is relatively easy (they may actually look forward to it); to others the idea of disappointing their current employer is gut-wrenching. A few things to keep in mind: first, very few people actually work for one employer their entire career so odds are the person you dread giving notice to has done the same thing at some point too; second, the anticipation is much worse than the actual delivery. In fact, people often feel a tremendous sense of relief as soon as the words leave their mouth.
Life is too short to tolerate a less than ideal situation just because you might feel guilty about leaving. If you really care about your employer (the people you work with that is) you would assume the admiration goes both ways and that they would want you to be happy. You should also remember that this is just a job, and that there is nothing stopping you from staying in touch with your colleagues.