If you liked the guy, and he cannot forget the ex-girlfriend in any way, have patience, do not demand from it reciprocal sympathies. You have to be near always that he got used to you. You need to prove to him that you are not worse at all than that with which it had relations.
If you understand that that young man who very much is pleasant to you is still in love with the ex-girlfriend, continues to suffer because of parting, have patience. Are not ready to wait, be near, stand his indifference and coldness - step aside better. If you in this situation require from it attention, to state claims and to take offense, then will only push away from yourself the young man. A bigger mistake will be if you begin to compare yourself and the former girl guy, constantly to remember her name to it. Try to invite more often him somewhere to populous places better: in theater or at cinema, on a visit to friends or in club, on dances. If its time is most loaded by interesting affairs, hardly it will have a desire to sit alone and to pogrustit, look at old photos or to dial the phone number of the ex-girlfriend.
You do not speak to the guy badly about his former beloved at all. It, most likely, will cause irritation or even aggression from its party.
You speak on some other the interesting its topics: about its favourite band, about sport, about study, etc. Most likely, you should read a lot of literature and to learn about the subject interesting it more to have an opportunity to surprise the young man with the erudition. Prove to it that you the interesting personality what you with it have much in common that you are close to it on spirit the person. Find also some common with it cause. For example, if he loves sport, register to the same gym and you go together with it to trainings. You watch the appearance: be bright, fashionable and stylish. However do not imitate style, appearance of the ex-girlfriend of your guy at all. Try to look so that paid attention to you. If the young man notices the delighted looks of men darted at you to him your attention will flatter. Most likely, he also will be able to look at such young person on the other hand: not as on the friend and as the charming girl. Do not show the negative sides of character at all: do not raise on it the voice, do not demand everything and at once. Your assistant in achievement of the necessary result (reciprocal feelings of the person who was pleasant to you) is time. Be patient.