When one's longstanding and upsetting non-sex life is addressed through masturbation, which, instead of offering relief or escape, exacerbates the situation, by reminding the person he/she is all he he/she has and likely will ever have.
After the supermodel party had ended, Hamish, as always, returning home alone, took matters into his own hand, as always. The production said and done -- looking around at his filth-nest of an apartment, the mountain of unwashed laundry, the tatty Led Zeppelin posters and the soiled sheets -- it provided no relief, proving only to exasturbate the awful finality, the unending and grave awareness of his apparent lot in life.