1.they have a history.
2.you can see it in both neal's eyes and alex's eyes how much they mean to each other.
3.the flower paper(it's their thing)
4.she know that she can trust him(unlike sara).
5.she knows him better.
6.he knows her better.
7."you saved me again"neal to alex (2x16)
8."you saved me"alex to neal(2x16)
9.they get each other better,they understand each other better.
10.they way they look at each other
11.it's obvious that she's in love with him.
12.it's obvious that he has feelings for her.
13.the hug in s2 finale.
14.the kiss in s2 finale.
15.with sara it's one sided and you can clearly see it(sara is into neal,but he isn't)
16.they have a much better chemistry.
17."you know i won't let anything happen to you"neal to alex.
19.neal was upset when alex asked mozzie to help her and not him.
20."kate,is goen the rest of us are still here"alex to neal.
21.she trusted him enough to give him her family's music box.
22.he was the one who helped her get to her family's treasure.
23.she's been there sinc the beging.
24.They finish each other's sentences
need to say more i think not