[morethanpretty]

Nope, be a private person, its a good thing, especially in the job force. Plus women love a closed off man, they like the challenge of trying to get him to open up to her because she's special to him. (I'm kidding, that's not really a healthy mentality on the woman's part.)
Why do your friends deserve you to open up to them? I don't see how you could possibly owe them emotional vulnerability. Be comfortable in who you are and the actions you take, there is no reason to feel guilty for being an introvert, although our society often seems to make it seem like a bad thing.
I don't really judge people based on if they stick by me in times of need, then again I'm used to flaky friends and being the only reliable one, so I tend to be very forgiving. If you want a friend who you can truly rely on to stick by you in times of need, get a dog. (Sorry cat lovers, they're awesome but also flaky.)

If I seem harsh or like a misanthrope, that's kinda how I am. I fully accept this about myself.