Nueng is so desperate to be loved that he kisses Ben in the music room despite his love for Palm. Nueng is so desperate to be loved that he kisses someone he doesn't love and lashes out at the one he does because he doesn't know how to hold onto that feeling.
Nueng needs to be loved, he needs a chance, he needs to know that he is loved and he doesn't have the self-esteem or self-love to wait or chose.
He had to kiss Ben because he had to be that desperate to be loved, to have a chance at being loved, to have the illusion of being loved.
Nueng is desperate and lonely and he loves Palm but he is certain Palm is straight and so he lets Ben kiss him, he lets Ben flirt with him, but he gets drunk and demands that Palm dances with him, not her, demands that Palm stay with him, not her.
Because Nueng is desperate for love but he's also in love and that's even worse because it means that none of the love he's desperate for is filling the void of the love has already has.
Nueng is still grieving his father and the family he's lost to the chaos after his death; he is still grieving the mother he loves who is now too busy for him; he is still grieving the youth and freedom he had that will never come back and now he is trying to he grieve the relationship with Palm he imagined.
But Palm does love Nueng. It's Nueng's own view as himself as unloveable that is leading to him grieving a relationship he can have as already gone because he assumes that Palm is flirting with girls and not him.
Nueng's gilded cage as left him defenseless against this pain because no one is looking at him in his gilding and wondering how hurt he is.
