Most people that have been through even just high school will probably say that they won't give it away easily... we've all been stabbed in the back and betrayed before. I'm not talking about the kind of trust where you'll give someone you're credit card number to purchase tickets online for you (..I hope you'd think about that for a looong while before doing so), because the idea of that is rather understood, I'm talking about the trust you give people when you lean on them with your thoughts and feelings... where you suddenly let yourself depend on someone else for comfort.
I've been there. Where you lean on someone for many things and one day they're just gone; it's terrible. We've all been there. But then I got to thinking... isn't that somewhat my fault? I've been in this situation a million times, and every time it hurts just as bad. I KEEP telling myself I won't do it again; and then I do.
The fact is it's very hard to find genuine people. That's what makes genuine people so special and hard to lose! Even being able to back your friendship or relationship up with X amount of years might not mean you can trust that person. Be careful. Not overly-cautious to the point where you're becoming anti-social and not trusting a single person, but be careful. Take the time to understand exactly who it is you are becoming close with.
But here's another alternative... which is rather obvious; strengthen yourself! Leaning on someone else obviously makes life a lot easier. We are social creatures, it's part of our nature to do so, so we should! BUT if that person becomes someone who we cannot trust any longer, we need to be able to walk away as unscathed as possible... because that sort of thing can happen out of the blue for any reason.
This is what makes break-ups and heated ends to friendships so hard... I saw this idea on a picture someone shared on Facebook today: it's not always the PERSON you miss, it might just be the feelings. So, be strong, and be able to walk away happy knowing that you can always meet other people to provide you that comfort... and if all else fails, you have yourself.
Enjoy life, and fill it with people who help you do so, but stay strong. The only person you can ever trust completely is yourself.. so use that to your advantage!