Who does he like?
If you want to get a guy who's in love with another girl, don't try and compete with it, it could cause you to have a strong jealousy, and she, in turn, will prevent you to function properly. Before to get a guy, find out who this girl is, whether you have chances of success? Find out how serious the relationship? Are they happy together? If you realize that they love each other, think about whether to intervene in their relationship? If it turns out that they are just friends, you have good chances to get your boyfriend back.
Find out your ex better
If your ex-boyfriend started Dating another girl, you probably don't know all about it, perhaps he is not getting from you what to expect. Often try to be with him, for example, if you are studying in one class, participate with them in common projects that are interesting to him, show interest in his endeavors in various businesses. Find out what he likes to do in his spare time, if you have any common Hobbies.
If you learn about new Hobbies with her ex-boyfriend, for example, sports or some Hobbies, try to study the issue. Show that you have similar interests with him, and help myself naturally. Don't stress that you are doing it especially for him.
Become a friend for him
Regardless of why you broke up, if you want to get a guy, you need to become a better friend to him. In no case do not discuss with him his current girlfriend, do not insult her and do not tittle-tattles. Your task is again to impress him.
Honestly answer the question about his feelings for ex-boyfriend. Do you still love him or is it jealousy and you just hard to see him with another girl. Don't mistake your feelings, they can lead to a new breakup.
Take your time
If you become good friends, do the next step. Often arrives in his company, visiting with him various events (sporting event, theater, etc.), hint to him about the date. But don't be too pushy and take your time, your suggestions are initially should be friendly and innocent. If your relationship with ex-boyfriend with his current girlfriend not too serious and you are able again to reach out to him, his return to you will be only a matter of time.