You ask "How do people manage their feelings successfully and not let their insecurities affect their relationship"?
They don't. We all try, but we are the sum of our past experiences and they effect the way we feel and act.
Being in love with someone, trusting them with your most vunerable of feelings, IS scarey. But worth it, when you find a good person. It doesn't hurt to question your feelings to check that you're sure, but don't battle your feelings. If it doesn't feel right, then back away. But if it does, then go with it. Take it slowly, talk it through, take care of yourself and don't take stupid risks (with your health etc).
But to say that you're scared of falling in love because you're afraid of getting hurt is like saying you're afraid of smiling 'cause you might get laughter lines. The gains far outway the losses.
We're all scared. Good luck xx