You should always be as open and honest as possible with people you love. Life is too short to do anything else. If they don't feel the same way about you and don't believe they ever will, it wasn't really destiny. At least you'll know, so you can begin to move on with your life.
As for being friends with someone you're in love with, it's possible, but difficult, and you should still be honest about how you feel. If you told them how you feel and they don't feel the same, it's even harder. Hiding something like love rarely works. Most people can't pull it off. They cry about being stuck in a "friendzone". Which is a completely meaningless term that they use to make themselves look like a good person. But really, the friendzone people are being selfish. They hang around their "friend" because they want something from them, not because they're interested in friendship. They complain endlessly about their "friend's" significant other, claiming that they're a scumbag/bad person. They talk about how they do sooo much for their "friend", but they're not getting the romance they think they deserve in return. It's all very sad. Don't be one of those people...
So, if you're going to be friends with someone you're in love with, you have to follow some rules:
The friendship is always more important than your romantic feelings. Always!
Respect your friend's decisions, including and especially their choice of significant other. If you can't do this, then you can't be their friend. It's as simple as that. It doesn't mean you have to agree with all their decisions, but you have to respect them.
Never, ever do something nice for your friend because you think it'll buy you some kind of love points, or because you think it'll get them to change their minds someday. Chances are, they won't change their mind, and you'll just end up here telling people you've been "friendzoned" Do nice things for your friend because they're you're friend.
Always be honest about how you're feeling, with yourself and with your friend.
Try to move on romance wise: There are other people out there. Hanging around someone you're in love with can be like torture, so you have to resolve these feelings, for your own good and your friend's.
I've seen a lot of people come through here who completely failed at only being friends with someone they have romantic feelings for. Very few of them followed any of those rules, and even the people who followed a few still failed. I don't blame all of them for failing, because it is hard. You have to be careful, and always put the friendship first.