QuestionI'm wondering if it's wrong to give a boy an erection? Since erections are related to "turning a guy on" and sexual thoughts, which sounds unpure. During slow dancing, I felt my boyfriend's erection. Also, when we show physical affection by cuddling, hugs, or kissing I sometimes feel him have an erection. Is he just too horny? Should I lessen physical contact that turns him on?
Most girls don't realize that erections in boys are a part of the autonomic nervous system. This is the part of the body that controls functions that are below the level of consciousness. Other examples of autonomic responses are: heart rate, rate of breathing, digestion, salivating, sweating, and eye dilation. The body automatically responds to conditions without conscious thought, though we can sometimes trigger changes by thought, such as thinking about something scarry to get our hearts beating faster. But notice that it is an indirect response. You don't think "I'm going to make my heart beat 120 beats per minute." You focus on a situation where the heart normally beats faster and the body responds.
Young men, in their teens and twenties, have little or no control over erections. In fact, the plague of adolescent males are spontaneous erections -- erections that come, often frequently, for no apparent reason. As a male grows older, he slowly gains some control over his erections but generally it comes with conscious effort and takes practice. Yes, sexual thoughts will trigger erections, but so will arousing situations, such as holding hands with a girl for the first time or holding someone close. Thus, your boyfriend is having typical reactions for a young male.
You should not be purposely attempting to trigger sexual arousal in your boyfriend. That is why Paul stated, "It is good for a man not to touch a woman" (I Corinthians 7:1), where touching is referring to sexual touching. When males are aroused, they have a harder time thinking clearly. It is easier for them to fall to temptations to sin. As Christians, we should be striving to help people avoid sin.
Understand that he is going to experience erections regardless, but when you know that your behavior is contributing to his arousal, you should back off -- for his sake and your own. Sex belongs in marriage. Tempting someone into lusting for sex before marriage is a sin (Matthew 5:28).
Since you are changing how you behave with him, you need to explain your concerns to him and what you plan to do about it. Hopefully he is a decent young man. He likely has been struggling with himself and his thoughts and will appreciate the reduced demands on trying to control himself. If he isn't a decent man, it would mean that he has been purposely trying to get you to notice his aroused state in hopes that you will give him sex. Either way, you need to know what you are dealing with so you can take appropriate measures not to get led into sin.