Umm if it's a pool party why can't you wear a bathing suit? Do you have your period or something? If so just wear a tampon or pad with like little shorts on top. If it's something else just comment my inbox maybe i can help.
Otherwise to get his attention just be yourself. Come up to him and talk to him. Smile ALOT! Look his way. Flirt with him a little. Try flirting with your eyes or something. Give him a nice friend hug and if he likes it he might make it into something else. If you need more ideas on like what to wear or do just comment my inbox.
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