Wow. I really enjoyed this Elle. And the second person worked very well for me. It didn’t feel at all self-conscious which I think it often does. It also reads as though it was written by an English native.
A couple of very minor points:
Sam throws up his arms a couple of times in swift succession which jarred for me.
This bit – His lips on you skin all evening quickly receded in her mind, so you held on to the last kiss he had left on your skin. You don’t search for the moment it was agreed that you were going to the cinema, instead you look for a dress to slip in. – It doesn’t quite make sense. I think the ‘you’ should be ‘your’ and the ‘her’ should be ‘your’ too. And you’ve slipped into the present tense in the second sentence. Even with the corrections, there’s something not quite right about the first sentence.
On first reading that was all I picked up on. I will try and read more closely later and see if I notice anything else.