Why Does One Experience Penile Pain After Nightfall But Not After Masturbation?

Hii.. So this is about my boyfriend..whenever he has a nightfall he experiences pain in his penis..and if he masturbates again he doesn t feel any pain..why is that..?? And one more thing..once I gave him a blowjob..his semen usually is kinda salty but at that day it kinda was bitter..why is that??