The principles of lust
are easy to understand
do what you feel
feel until the end
the principles of lust
are burned in your mind
do what you want
do it until you find
These lyrics pretty much say it all as far as promiscuous behavior goes, whether one is straight or gay. Often, the underlying desire is to find love, to be loved. The reason acting upon lust is gravely sinful for anyone, is that sexual acts, separate from the procreative act are disordered, in so far as they endanger the preservation and propagation of the human race. (The same reason, BTW, contraception is evil.) Nevertheless, this is clearly revealed in the homosexual, as well as amongst heterosexuals who engage in disordered sexual practices.)
Today many people indulge their lust by the use of pornography, which is also a sin. The reason impure thoughts and sensual delight in pornography is disordered, is because these indulgences tend to unrestrained passion, leading to promiscuous behavior. It is often said by people with SSA that sexual expressions such as auto-eroticism, viewing or reading pornography, which is a form of voyeurism, is okay because it doesn't involve another person. That is untrue. Lust, of itself, when consented to, is a grave sin.
"The lamp of the body is the eye. If your eye is sound, your whole body will be filled with light; but if your eye is bad, your whole body will be in darkness. And if the light in you is darkness, how great will the darkness be." - Matthew 6
This is just a follow up to the Fudge Packers post.
Art: "Love and Lust" - artist unknown.