Most Helpful Guy
Doesn't sound like swimming was a good idea if you're not ready to tell him about all that. Hopefully he has the good taste to not ask any questions and just enjoy your company.
If he does ask, you have two choices. Be honest or tell him you aren't ready to talk about it. Both risk turning him off. If it were me I'd rather that you told me, because having someone open up to you feels good.
Most Helpful Girl
wear something that covers you up if it makes you feel better.