Whenever I kiss and press my lover's breast my testicles hurt a lot. Why is it so?
"Marriage is honorable among all, and the bed undefiled; but fornicators and adulterers God will judge" (Hebrews 13:4).
I assume you are not married and thus you are engaged in lewd behavior. "Let us walk properly, as in the day, not in revelry and drunkenness, not in lewdness and lust, not in strife and envy. But put on the Lord Jesus Christ, and make no provision for the flesh, to fulfill its lusts" (Romans 13:13-14). It is not right or proper for a man to be sexually touching a woman he is not married to. "It is good for a man not to touch a woman" (I Corinthians 7:1).
The reason you are feeling pain in your testicles is because you are holding an erection for too long. Erections are caused by a small muscle clamping down on a vein bring blood out of your penis and back to your heart. Blood comes in fast, but goes out slowly causing the penis to inflate like a balloon. After a while the cells in your penis and scrotum, which share the same blood supply, start to protest because they aren't getting enough fresh oxygen. This is commonly called "blue balls." This is what happens when a man holds an erection for a half-hour or more.