should I go ?

I'm really good friends with a boy I've known for a while now - we "dated" when I was 12/13, nothing ever serious. I find him really attractive and a bit of a flirt, he's in a two year relationship with a girl - he's admitted to me several times now he's not entirely happy with her (I think he's with her because he's scared of being alone). We talk a lot harmlessly, but every now and then he'll send a flirty message or imply something. Tonight he's said 'we should go for drinks' and I'd really like to go but that attraction is there between us - should I stay way clear or am I reading into it too much ?