If the person is already in a relationship then you should not think about that person more than a friend. It will take you nowhere and rather you will hurt yourself. Just see around. There are so many people whom you will like, the only need is to know them. You should be good friend with that person, in this way you would not lose the relationship with the person you like. But certainly you should not impose yourself on the person. And you have written that you like that person. Dear we have so many persons in our life whom we like, so what. Nobody can stop you from liking or loving any person but you can’t expect the same in return. Just remember this.