Keep a journal
From time to time we all need to bitch about clients, suppliers and colleagues. When you work alone there is a sometimes a danger in that any human contact becomes a surrogate for these 'office conversations'. Before you know it you're spraying your world with indiscretions.
My solution is to keep a journal. That's a grand name for what is actually a series of MS-WORD files kept very separate from my work folders on my computer. I don't write every day, only when I feel compelled, but when I do I allow myself to write down absolutely anything I'm feeling. Because no one else will ever read these pages I can use them to hope, plan and most importantly vent.
Writing honestly is its own reward. Over the ten years I've been doing this I've assembled a record of conversations with myself that is now a genuine resource. Let's say I'm nervous about an upcoming meeting, I can easily review how I felt last time I was in a similar situation; what did I write before the meeting and what did I write afterwards? What went well and what would I have done differently?
We've all heard the Socratic quote, 'An unexamined life is not worth living'. Isn't one of the joys of self-employment the opportunity to live an 'examined life'?