Although I consider myself an introvert, I will open up to almost anyone who is near when I have an issue weighing on my mind. For instance, whenever ABM does something that I think is stupid or insensitive and I don't feel like I can talk to him about it without causing a fight, I vent to my office mates or my movie gals or whoever is with me right after it happens. Then I feel bad that I've opened myself up to people who aren't going to be in my life for the long haul, and for the next few days I will cut myself off and keep quiet to avoid talking too much.
I imagine most people vent about their family issues to their siblings or their best friends. In my case, my sister and my BFF both live far away. I don't feel like I can call them and take up 30 minutes of phone time just to vent. You call faraway relatives if your kid got into a good college or if someone landed in the hospital.
Others use their blogs as a platform to get these sorts of issues off their chests, and I used to do that once upon a time, too. However, now that we are in the Facebook era of everyone looking online to find out all your dirt, it has become unfashionable to use your blog as your open diary. According to the "experts", I'm supposed to be afraid that what I write in this blog will keep me from getting a job someday. So I don't vent too much here, either.
Finally, I do believe there is merit in the idea that marital concerns should stay within the confines of the marriage and not involve other people. Still, it is difficult when I have thoughts on a subject and I just want them to be heard by someone.