You will know the person loves you because they will tell you. The tells come in small ways, compliments, nice things said about you, your appearance, long silences wanting to be filled, from looking in the person's eyes. If the person does random unexpected things for no reason, and gives you presents, or is around you a lot. Make excuses and find ways for the person to be around you as much as possible, to help them person feel more inclined to want to tell you and be comfortable with you.
Create the opportunity for the person to tell you in some way. But you must tell the person that you love them first, and then give them time to soak it in. Love can go 2 ways - they will reciprocate and return the love or not. You have to be prepared to be given a no also. Love is fickle.
I hope this helps you some how. And best wishes - I hope it works out!!! :)