This is very true, and unfortunate. It makes it easy to feel like everyone is being successful except you. I realized this a couple years ago and, when talking to other founders, I just stopped sugar coating things about my situation. I would tell them about our struggles, what was going on, and its affect on me. I don't think I've ever been brought to tears as many times as this year. It is super painful, but lying about it is bad for all involved. You can't get the support you need, nor provide proper support to others.
I can definitely vouch for the dark days. I feel fortunate to be an eternal optimist who knows these things are temporary, but the startup lows are about as low as they come. On top of that, you have things like breakups, family emergencies and other tragedies that are already hard enough to deal with when you are not nursing a struggling company. When those things hit at the same time, it can feel impossible to do anything.
Seriously, as a founder, find a few people you can really confide in and do so. And, don't be afraid to say things aren't going well. You never know what people can do to help. On that note, though today isn't the best day for me to cheer up others, I'm available to chat for any founder going through dark days. joey@earbits.com