Pleasure is primarily associated with the physical. It is solely in the realm of the mundane plane. Though HETEROSEXUALS do, HOMOSEXUALS do not interpret pleasure as love itself, only as a limited aspect of it.
The emotional letting associated with pleasure is extremely ephemeral and can be reduced to a quantitative accumulation, in that its "lasting" achievement is marked by a necessary repetition of physical acts which are a measure of its efficacy and longevity. Hedonism is it in its most refined quality.
Happiness, on the other hand, is mainly felt in the psycho-spiritual realm. It is, if you will, an otherworldly state of being and, often, can exist in an individual over a greatly extended period of time, if not a lifetime. It is a qualitative phenomenon that, once becoming one with it, is not subject to the vagaries of time or ephemeral physical sensations.
These experiences, correctly given and received, only serve to enhance its presence and increase the level of one's awareness of self and reciprocal obligation to others. Selfless love and godlikeness are its finest manifestations.