I'm in a relationship and I want to know if I actually sleep with my girlfriend -- no sex, just sleep and cuddle with her -- is it sin and why? If we are naked together -- no sex just kissing and touching each other -- is it sin and why? Is oral sex sin and why?
I really want to know because I really love her and respect her. I want to have that trust with her and I really do want to marry her if God wants it. I want to respect God to, so that's why I want to wait for marriage to make love to her.
Let's start with the fact that you want to save sex for your wedding night. That is what you should do because it will make it all that much more special and important. It is also important if you want to please God because He said that sex outside of marriage is wrong. "Marriage is honorable among all, and the bed undefiled; but fornicators and adulterers God will judge" (Hebrews 13:4).
Sex isn't just when a guy puts his penis into a girl. That is the end point, but sex includes all the things that leads up to that point or is done in place of intercourse. The reason why it is called oral sex is because it is still a form of sex; thus, it is still fornication. See: Is oral sex before marriage OK? for more on this topic.
Next, let's look at being naked with your girlfriend where you are kissing and touching her. Such touching is getting the body ready for sex. The word for it is called "foreplay." It is the playing around with each others bodies before sex. The touching triggers reactions in both the guy's body and the girl's body to prepare for intercourse. What you aren't counting on is that one of the changes is that the judgment center of your brain goes offline when you get heavily aroused. You do things because it feels right at the moment, even though you know you shouldn't do it. A lot of people have gotten caught in this trap. You have every intention of not engaging in sex, but the next thing you know you have your penis in her and ejaculating. After all, if things get out of hand, what is going to stop you? Even if it doesn't happen the first few times, each time you'll get a bit closer to doing it until eventually it does happen.
The playing around with someone's body in a sexual way is called "lewdness" in the Bible. "Now concerning the things of which you wrote to me: It is good for a man not to touch a woman" (I Corinthians 7:1). The reason you should not sexually touch a woman is because it naturally leads to sex, which should not take place when you are not married.
But think about this as well, what is going through your mind as you are fooling around? I'm positive it would not be about getting tomorrow's homework done. More likely you would be imagining what it would be like to go ahead and put your penis in her. In other words, you would be thinking about committing fornication and trying to come up with a reason for going ahead and doing it. That is called "lust." Think about doing something long enough and you'll convince yourself that it will be all right to do it. "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). See: Is foreplay wrong if it doesn't lead to sex? for more details.
If you are sleeping with your girlfriend, then do we assume you are not wearing much? If you are alone in a room, what will stop you from doing more than just sleeping. After all, as you fall asleep, your body gets aroused. This is where wet dreams come from. With you being highly aroused and having a girl in your arms, what do you think will naturally happen? "Can a man take fire to his bosom, and his clothes not be burned? Can one walk on hot coals, and his feet not be seared? So is he who goes in to his neighbor's wife; whoever touches her shall not be innocent" (Proverbs 6:27-29). Though this passage is talking about adultery, the overall point remains the same. Let us assume for the moment that despite your intentions, several months from now you slip up, give into temptation, and have sex. Would anyone say that it would be an innocent "accident?" Ask anyone on the street and people will say that it is an "accident" waiting to happen and that deep down you knew it would happen.
When it comes to sin, we are not suppose to see how close to the line we can come without crossing over. A Christian's response to sin is to flee from sin. "Flee also youthful lusts; but pursue righteousness, faith, love, peace with those who call on the Lord out of a pure heart" (II Timothy 2:22).
But if we have to flee from sin, doesn't that mean not doing anything? Because meeting people leads to love, love leads to romance, and in today's society one cannot get married being to young. Back in the days you could get married when you where 15 or 16, and that leads to premarital sex that leads to sin.
Love does not necessarily lead to romance. You love your parents. You love your family. You may even love your aunt Bertha. But none of that leads to romance.
I'm not certain how you define "romance." I've notice a lot of people think love and romance are physical actions, but they aren't so defined in the Bible. Look through I Corinthians 13:4-8 and you'll see it is about the treatment of others, especially when you are not being treated well. It is that type of love that becomes the foundation of lasting friendships and with a special woman, a marriage.
While society, with all of its whims, doesn't currently encourage marriage at a young age, a couple can get married at the age of 18 in most countries, including the United States. No one is forced to wait. But if you respond, "I'm not ready to marry yet," then it should also be true that you are not ready for the responsibilities that result from having sex with a woman.
It is the assumption that sex has to happen -- that it is inevitable -- that is false. Love grows and develops best when it is not first expressed in a physical manner. Getting involved in sensuality and sex actually detracts from building a relationship because it ends up dominating everything.