I didn't tell a single member of my family, nor any of my friends, that I was writing a book. I didn't say a word about it to anyone, in fact, until it was published. Now I self-publish, and I still find it difficult to talk about my current projects. I'm used to going it alone, but I've learned that it's the absolute worst way to go about writing.
Writing anything is difficult. Writing a book is an exercise in self-torture. And writing a good book takes more than what you currently have inside of you. If you're going to write something great, you're going to need other people in your life to help you get through it. At the very lest, you're going to need someone who can remind you to eat something every once in a while.
I've gone on record saying that you shouldn't really talk about your book projects while you're writing the first draft. You don't want to be influenced by other people. However, once that first draft is finished it can be invaluable to check your ideas against another person -- before you open up the field to every book reviewer out there. Someone close to you is going to be a lot nicer about pointing out plot holes than I would be, for example. I'm pretty picky, and I'm really nice compared to most people who review books.
You can write a book unsupported, and publish it, too. I know this for a fact. But I also know that you're going to write a better book if you have someone else that you can talk with about it, if you have someone who can read it, and it there's someone around to remind you that you should eat something.
Don't go through your writing career unsupported. Reach out to people in your life. Reach out to forum groups. Reach out with your ideas and your thoughts, and write better.