HOW CAN I INVITE HIM?!?

OK me and this boy dated for 2 years and we recently broke up, but we realised we didn't like things without each other so we have started 'seeing' each other. My friend Lydia is having a party coming up with a few people going and getting drunk. Lydia said it would be fine if I brought him along so how could I ask him? This sounds really pathetic but I'm not very good with things like this..I want to say something like 'What you doing Wednesday night?' and then invite him to the cinema and then casually ask him afterwards if he wanted to come along? or would that be too last minute? please help, thanks guys <3