i think you answered your own question, he is shy..
its ok, being out, you can relax, but when your together with no one else, its very intimate, in a social sense, and his shyness probably takes over, as for the not contacting, its a bit strange, but he may feel like he does not want too seem too overbearing, some people just dont make contact unless they are contacted first, if he was just after you for sex, it would probably be the other way round
just get very drunk together, that normally helps loose inhabitions