1.) Make your sister wear really ugly jeans
Nothing makes a girl feel better than seeing her sister look worse than her, so encourage her to buy a pair of stupid jeans. If they can somehow make her extreme thinness work against her, all the better!
2.) Pet some salukis
As everyone knows, salukis have magical healing powers.
3.) Work out by the pool with a poster of yourself behind you
You'll be so tired from your workout and so weirded out by the poster of yourself behind you that you won't have time to think about your public, humiliating breakup. Also, make sure you use the lightest weights possible.
4.) Match your sunglasses to your bikini
It will probably be the most challenging thing you've done in a long time, so it'll take your mind off what's-his-face, plus brain-games like that help stave off Alzheimer's!