Josy's clearly been with guys before, it's just a question of how many before she got together with Maya.
I could also see Josy still being with a guy (or guys) after that camping trip since just because she and Maya got it on a bit doesn't necessarily mean they started a relationship right then and there. Josy seems like the kind of girl who took it all in good fun and probably looked at it as just that, but Maya took it more seriously. So, when they got back to school, Josy carried on as she had always done, maybe hooked up with a guy or 2, and Maya was hurt by this, and when Maya let Josy know that it made Josy realise she felt more for Maya han she had first thought.