You can't make men want you back. Well not genuinely. It's called manipulation and it never works out well in the end!
BUT, if you want to make him wonder whether he made the right choice though. Be and act positive. Dress up fab (NOT cheap! ) and have a good time with your cousin and mates. Show him that it's his loss that he stopped associating with you and you can take him or leave him. Socialize, smile, laugh, flirt with everyone there and even go and do the same with him. Not in a secluded one-on-one kind of way, but if he's there in a group, go and talk to them all. Show him that you're not bothered. Hope that helps.
Be nice to him, flirt, and see if you can get him to hang out with you some other time. If he hesitates, he might not be interested. But if he seems surprised and excited, he probably still likes you and there is a good chance you can get him back. If not, you might want to forget him.
Yeah, I know...astrology and horoscopes...fiction. But it was eerily accurate for me and who cares whether the stuff is real or not. If a reading helps you figure out what you really want (and who you really want and whether you want to spend time getting this guy to like you again), then it doesn't matter where it comes from.
I wish you all the best with this situation and I hope this helps.
The best way to do it is to first look killer hot like absolutely smoking but not too revealing or overdone, this makes it obvious you're trying. Guys can be easily persuaded by aesthetic beauty.
But seriously, to all the girls out there it's not only that.. you have to be the bigger and better person inside as well. If he can see right through you as a person with maybe low self-esteem or low self-respect it isn't going to work. You have to be a strong woman and prove not to him but yourself that you can have a great time at this party because you're a fun person/friend and a great gal. And you're perfectly happy without him in your life. It's a bit of a paradox.
To get a guy to want you or like you back, you've got to wear something that makes you look really irresistible and flirt with another guy in front of him but don't be mean to the "guy" but act a little oblivious to his presence. It's bound to work! This happened to me and I know exactly how you feel right now! Some guys can be real JERKS! Don't smile to him too much or he won't respect you- he has to know you were sad when he just stopped talking to you. Follow your instincts, does this guy even deserve you back?
If he does try to work on the reasons the relationship went wrong, didn't see each other enough maybe?
Start talking to a guy friend. Get him to go along with it. Get him to make you laugh and put his arm around you. Get him to hug you and kiss your cheek. The other man will get so jealous and he'll wish he never left.