Is two single people of opposite going away together on holiday a good idea?

You sent some pretty mixed signals with letting him pick out your swim wear, specially with what he picked out. Sounds like he may be expecting more from this weekend then you are willing to give to him, and that was totally from your end. Sit down and explain to him that you hope that you both can enjoy this weekend, but that you aren't looking for any romantic interludes right now. Then take the bathing suits back and pick out something you want to wear. If he throws a fit about it, meaning he hems and haws, or gets offended over it, then he really WAS hoping for something else and you shouldn't go at all.