The orgasm is more than a physical act. It is a psychological discharge of spiritual energies.
Remember that there are three mercuries: the brute mercury (physical semen), metallic soul of the sperm or ovum (sexual energy) and the mercury fecundated by fire (the spiritual flame of Christ, the Kundalini).
Of course, discharging the physical semen will discharge the sexual fires and energies. However, one can orgasm while retaining physical fluids, and yet it is still a sexual discharge or explosion (loss of subtle mercuries).
There are many excuses made by so-called "spiritual" persons who justify orgasm without loss of the seminal fluid, ignoring that even if the physical seminal fluid is retained, the loss of the metallic soul and sacred fire of the sperm still occurs. These people are practicing black magic (which is always defended by many sophisms of the intellect).
For thirty years I sought God. But when I looked carefully I found that in reality God was the seeker and I the sought. -Bayazid al-Bastami