Sidenafil citrate

A delightful tale, well written - and a nice 'twist' on the old 'snowbound at Christmas' theme! I gave this one a solid '5'.
To the commenter (Sex4lf57?) who said that Viagra doesn't work this way, I'll toss at least a cautionary comment or two.
Viagra is derived from a medication (sildenafil citrate) that was originally designed for cardiac patients. To prevent stress on the heart (that can cause a heart attack), the chemical causes the capillaries in the body to open as wide as possible, allowing the blood to flow freely with less pressure being applied by the heart.
As such, it also opens the capillaries in the corpus cavernosum of the penis, which leads to an erection. Now, there's a 'valve' that limits blood flow to the penis, so as to allow urinary function, without urine being able to seep into the passages where sperm travels. When a guy urinates, the semen passages are cut off - and when he is erect, the urinary tract is cut off, because the urethra (tube in the penis) does double duty.
When there is sufficient erotic stimulus to cause that 'valve' to switch the seminal tract to 'open', it also opens the sphincters that control blood flow to the penis, so that the capillaries can inflate completely.
During the years (nearly 60) that sildenafil citrate has been in use in cardiac patients (under another drug-name), it was noticed that when a patient was taking the drug, he was more susceptible (at an older age) to more-solid erections. Gradually, the doctors prescribing the drug got 'field reports' from their patients, and forwarded them to the company that makes the drug. Its use as an ED drug is secondary, and took a long time for FDA approval to market such a drug to non-cardiac patients.
When the person taking the drug is in their late teens or early 20's, and has a quite healthy circulatory system - and is around a near-continual erotic stimulus, as is the main character in this story - the effect CAN be a near-perpetual erection. Even the attempts to diminish it by masturbation won't necessarily cause it to go down, when there is a hotly-desired woman present and making subtle erotic comments to the male.