There is one time when I masturbated in my girlfriend's room. When my sperm come out it touched her underwear. I think it was the inner part of her underwear right where the vagina is located. Then I put it back in her drawer very deep. My question is that when she wears that underwear later, will she get pregnant?
The short answer is "no." Sperm cannot survive long outside the body, especially not once the semen dries.
Of course, it was also rude to soil someone's clothing and then try hiding it in a drawer of clean clothing.
But there is a more important issue. You have no business masturbating in someone else's room and with someone else's things. One, you shouldn't be exposing yourself where someone else might walk in. Two, you were involved in lusting for sex with your girlfriend. "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). Lust is strongly wanting to do what is immoral, which would include the fornication that was on your mind at the time. "Marriage is honorable among all, and the bed undefiled; but fornicators and adulterers God will judge" (Hebrews 13:4).
You're getting older. A part of that means you are responsible for your actions and the consequences that result.
OK. Thank you.
I want to behave myself, too, but I can't stop masturbating. Can you give me any advice to stop masturbating?
As odd this might sound, rather than tell you to stop masturbating, I want you to practice self-control. You get hungry, but you don't eat just because you are hungry. If you did, you would get fat. Rather, you use the hunger to remind you not to skip your next meal because you know you need it. In the same way, your body needs to ejaculate semen, but just because the urge to have sex comes upon you, it doesn't mean you should drop your pants then and there.
You have two seminal vesicles which are constantly producing semen. Eventually those vesicles are going to get full. The rate of production varies from man to man and the rate of production for an individual man, while somewhat steady, varies a bit by the amount of sexual stimulation he receives. Since your body, as a teenager, is still deciding exactly what constitutes sexual stimulation and since your hormones have not settled to a fixed level, the production of semen can be higher than an adult. When the seminal vesicles get full, needs to get rid of the excess semen so there is room to produce more. It does this through ejaculation.
The problem is that you lose control over bodily functions when you try to completely keep them from happening. For example, if you try to keep from urinating eventually it is going to come out whether you want it to or not and mostly likely the body's timing isn't going to be convenient for you. And in the meantime thoughts of needing to urinate is going dominate every moment. If you try not eating, you will eventually gorge yourself on food. And in the meantime, thoughts of being hungry is going to dominate every moment. If you try to stop ejaculating, eventually your body will take over using whatever means is available. But in the meantime, thoughts about sex will dominate every moment.
It is when a guy avoids ejaculating for a long time that he is most vulnerable to sexual temptations. He is dealing not only with the temptation itself, but also fighting his own body's demands. More guys give into pornography, or even fornication, when they try to not ejaculate.
The way to maintain control is to manage your body's functions. To control hunger, you eat reasonable amounts at reasonable times. You use the toilet at regular times and even plan ahead; I'm going to be busy for the next two hours, so I better empty my bladder now. Semen buildup in your seminal vesicles is no different. As you feel the edginess of sexual desire build up, you know you need to ejaculate. You can either take care of the matter the next time you shower or you can plan on having a wet dream -- ejaculating at night in your bed. If you are getting to the point where you feel like you're going crazy, then you are waiting too long.
What I would like you to do is decide where and when is an appropriate place to take care of your need to ejaculate. It needs to be some place private and it needs to be where you can clean up after yourself, which is why I suggest the shower. In addition, how you trigger an ejaculation matters. Looking at pornography or lusting after sex with your girlfriend is wrong because to do what you are thinking about is wrong. "For this is the will of God, your sanctification: that you should abstain from sexual immorality; that each of you should know how to possess his own vessel in sanctification and honor, not in passion of lust, like the Gentiles who do not know God" (I Thessalonians 4:3-5). The problem with pornography is that it warps your idea of what women and sex is about. Guys caught up in pornography see women as just objects to ejaculate into. Women are no longer people. Lusting for sex with your girlfriend also can lead to seeing her only as a place to put your penis, and you forget that she is a person whom you are supposed to care for and protect -- even from yourself. Therefore, while it isn't as exciting, treat masturbation as bodily function that needs to be taken care of once in a while. Do it mechanically without any particular thoughts about any particular person. When your seminal vesicles are fully, this isn't hard to do.