Most people are smart enough to realize that a workplace won't stay the same forever. It's a mix of people - people change with age & circumstances, some people leave, new people come in. When that 'groove' is good, those are some really fun times, even if the job itself sucks. Somebody much smarter than me once said "The only thing constant is change". Tattoo that on your brain, back, belly, whatever and you'll be much better, well-adjusted person for it.
Also, most (but not all) coworkers realize that you're doing this to better yourself, and shouldn't lay that particular guilt trip down. They SHOULD be happy for you, if they're not too caught up in themselves. If he/she is that caught up in themselves, is that REALLY a friend?