It would only be horrible if you did say it out loud to them, keep it as an inward thought and I don't see the problem, these are people who circumstance has thrown you together with - nice if you did like/admire them, but if not then OK.

I can see you feel out of control with how your health/life has gone & I don't intend to minimise the sadness you feel, but I hope in time you will work through this and adjust your goals and feel in control again.

As goes your co-worker, IMO talking about your personal situation is out of order & not conducive to a healthy working atmosphere, perhaps you might consider taking this to your boss? If your boss doesn't tackle it would you consider volunteering elsewhere?