Aww... shucks ((hugz))

I'm thinking maybe you could also read the notorious 'Rules' book. It helped me to have a different mindset about men and dating. I wonder what would happen if you would become more 'unavailable' and start dating other men? Or sign up for cool things or classes away from him? Or if you'd flirt with other men?
I'd definitely stop the cuddling, holding hands and kissing if you're not in a relationship and the situation is clearly making you uncomfortable.

Maybe go walking/running or doing some physical work or sports to 'let off steam' first, if you're gonna talk to him...
As for beginning the conversation - hmm.. Maybe you could just pull away next time he'd try to hold hands or do something physical and say, 'Hey, we're not a couple (yet) - or are we?' or something like that? 'Are we dating or just friends?'

There are people who are naturally flirty and will flirt with anyone, even if part of a couple. Not sure if he's one, or just 'not that into you' or you've been too available/giving so he's interested elsewhere. You'd have to ask yourself if you'd be willing to put up with this kind of behaviour, and explain if you're dating you don't like it that he flirted with that girl. Maybe he'll deny flirting and just say he was talking to her (and maybe he was, not sure, wasn't there. I just know sometimes people thought I was flirting when I wasn't, and was just expressing enthusiasm and talking in an animated way.)

((hugz)) again PS I'm single so take everything with a grain of salt.