It is not possible to make your heart not fall in love. However,you can prevent yourself from being in such a situation. This is by ensuring that you avoid the presence of that person or rather the situation that brings about those feeling. Ensuring that your mind is occupied through meeting new people and having fun can also help a lot.
You shouldn't stop what you feel about a person. Love comes once or maybe twice in a lifetime but it's not the same as the other. It' s better to love than to not have loved at all.. Who know's maybe this time you find your true love.