I was recently in a similar situation, although not in SV; you are feeling a lot of unnecessary guilt(?), from a logical standpoint you probably realize it is

I was recently in a similar situation, although not in SV; you are feeling a lot of unnecessary guilt(?), from a logical standpoint you probably realize it is not justified, but that does not mean you aren't experiencing the emotions. You just have to suck it up, and approach it like a chess game, plan your strategy, and ignore the emotional aspect, not to say you can actually flip a switch and not feel them, but do your best to just ignore them, and only let your brain do the work. To help with this, employers don't necessarily need you as much as you probably assume they do. They go through this a lot more than you, so it's not a big deal. If you are really afraid of burning bridges, give 4-6 weeks notice (that's what I did), and reaffirm, that you will help in any way you can (sitting in on interviews, helping the new hire train if they find one quickly enough, teaching current employees some stuff that will ease the transition irt what you were working on).