Lend a Hand
I'm not the type of person to share my belongings with others, or loan them out, since I'm particular about their staying intact and I don't want them to get ruined. So I'm having problems with the Torah idea of having to loan things in order to help others, and, even more, with the idea that I should somehow intentionally buy things for the purpose of letting others use them. Is this really a requirement, and if so, how can I overcome my natural inclination to keep my things to myself?
It is certainly understandable that you want to preserve the things that are important to you, that you bought for yourself to be able to use and enjoy, and not have to worry whether they'll be returned, and, if so, whether they'll be damaged or broken, or at least not available for you when you want them.
But first you have to ascertain whether that's your real motivation, or perhaps you're fundamentally uncomfortable with helping others.
For example, even if you don't loan out your personal belongings, are you willing to offer your help in other ways? If not, that needs attention. But if you're OK with that, then even before you lend your things, you can lend a helping hand. Work on finding ways to be helpful to others in ways that don't depend on lending your belongings.
That being said, while you don't have to give out your things to irresponsible people or under circumstances that are likely to cause damage, to normally responsible people in normal circumstances you should be more forthcoming in sharing. Judaism teaches that one's wealth (and therefore one's belongings) comes from G-d. And just as He shares of His with us, we are expected to share that with others. Doing so is almost a condition for His giving.
Yet, there is another possibility for you as well. If there is a certain thing of yours which people tend to need and ask to borrow, and you don't want it to get damaged by loaning it, you could buy another such item specifically for the purpose of lending it, while keeping yours for yourself.
This is the idea of a "gemach", a type of free loaning organization that benefits others by making things or services available to them which they normally don't have. In fact, a "gemach" might loan things that you don't own yourself, or have no use or interest in, but others do. This might include power tools, infant supplies, Shabbat goods or many diverse and various things.
So given your description of yourself, I would suggest finding other ways to help people while also loaning your own things a little more liberally. But perhaps more importantly, I encourage you to start a "gemach" or two or few to benefit others in this way. Usually, the costs of supplying, and even maintaining, a "gemach" can be covered by part of the money a person sets aside as "ma'aser" (a tenth of one's income) or for charity. Sometimes, a minimal fee or voluntary donation is used for upkeep of the "gemach".