Your question reveals a continuous struggle for Christian men and women. The Lord built our human bodies with a libido, with a desire for sexual fulfillment. Our sinful flesh wishes to give in to every sexual temptation no matter how big or small the temptation. On the other hand, God has commanded that the only proper outlet for sexual fulfillment is within the sanctity of marriage. "Marriage should be honored by all and the marriage bed kept pure, for God will judge the adulterer and all the sexually immoral." (Hebrews 13:4) The flesh desires to give in to sexual temptation. The faith desires to get away from sexual temptation. Your faith is warning you that a strong temptation is near. Since your heart is with your boyfriend, since your love is with him and since you are even planning on becoming married someday, then those wonderful truths will be used against you by the devil to tempt you and your boyfriend to push past God's boundary lines and fall into sexual sin. Your question mentioned briefly that you are concerned whether or not you have sinned by noticing that he becomes aroused. It is not necessarily a sin to have noticed he was aroused. The sin might be found in the answer to this question: how did you notice his arousal? Was there body positioning or "activities" going on that are less than God pleasing? The other question to ask is: What was your reaction after noticing his arousal...almost pleased, desirous to explore, turned on yourself? These questions are asked not to accuse. They are asked to show where the devil is tempting you to sin against the commands of Christ.

You also asked if he is not practicing enough self control. It is difficult to determine with absolute confidence if he is sinning for only the Lord knows his heart. Since you mentioned that you are both planning on becoming called workers, I'm guessing that you are either in the last years of high school or you are in college. That means your boyfriend and you are fluctuating in your sexual hormones and sometimes that means that a young man will very easily and sometimes without any warning become aroused. There are times it happens when there is no sexual thoughts even taking place because the body is adjusting to varying hormone levels. There are many more times when the arousal happens during sexual thoughts. This is why I can't say absolutely that he isn't practicing enough self control. With that being said, you mentioned that it happens when you are kissing or while watching a movie (his mind might be wandering and thinking about you or someone in the movie) which can cause his arousal. Thoughts that cause that instant of a sexual reaction are lustful thoughts. The book of Matthew (5:27-28) is very clear when it says, "You have heard that it was said, 'Do not commit adultery.' But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart." If that passage describes what is happening with your boyfriend as you are kissing or during your movie watching, then I would agree that he is sinning by not practicing enough self control.

So what do you do from here? If you are planning on spending your life with your boyfriend as husband and wife and also as fellow servants of Christ, then I am confident you both have a heart for following Christ's Biblical laws regarding sexual relations. Your boyfriend is probably struggling too. He may be embarrassed and is not sure what you think. I encourage you to talk with him. Let him know that you love him and that you are excited to continue your relationship towards marriage, but express also your love for your Savior and your uncompromising desire to follow his will. I'm sure he will have the same response, the same desire. If you have an open dialogue about this concern, it will be a common point of strength within your relationship. If not, it will make your time together become awkward and either your relationship will suffer or, more tragically, your relationship with Christ might suffer. Let the love of Christ dominate your conversation. Use "I" statements when you talk with him. "I feel this way..." "I am concerned that..." This will keep the conversation open and he won't feel attacked. Ask him what he thinks and what his feelings are. Read scripture together. It will help keep you connected to the reason behind your sanctified living and it will bring comforting forgiveness if errors have been made. Here are some suggestions for scripture readings: Psalm 32:3-5; Galatians 5:16-18; Matthew 5:27-28; 1 Thessalonians 4:3-6.

God's richest blessings on your conversation, on your relationship with your boyfriend and on your Christian walk towards serving Christ as a called worker!