Establishing boundaries in a relationship is an especially tricky thing in our culture. Needless to say, we are a very different culture today than existed 2,000 years ago, at least as far as relationships go. The very concept of dating is almost alien to the Bible, and yet, with a few exceptions, that's just the way things work now.
Because the relationship structure is different, one could say the boundaries established in a relationship are also different. But of course, the 21st century is not some kind of bubble outside of God's foresight. Everything we need to understand what a boyfriend and girlfriend can do in a relationship is available in scripture.
Within marriage, there are very few barriers. Obviously, there are still some, but marriage is pretty much the "highest" relationship you can have with regard to what a couple are permitted to do. You and your spouse have full rights and privileges, along with the accompanying responsibilities, all approved by God. By contrast, the Bible is very clear on His condemnation of sexual intimacy outside of marriage. It's called "fornication", and it's quite safe to say God really doesn't like it. No matter how deeply you may love your partner, no matter how "ready" you both think you are, no matter what type of contraception you use, you cannot morally justify pre-marital sex.
But what about non-sexual practices? Is it wrong to hold hands? To hug? To kiss? These are all difficult questions to answer, which is probably why so many different Christians give different answers. But I contend there is a way to answer Biblically.
Aside from marriage and friendship, the Bible does describe other male/female relationships. Father/daughter. Mother/son. Siblings. These are all relationships with the complementary gender. I contend that these are excellent benchmarks for establishing boundaries between unmarried romantic partners.
Just as the Bible is clear on condemning fornication, so also is it clear on condemning incest. You cannot marry your parent. You cannot sleep with your sibling. Close biological relationships (and those imitating such, e.g. step parent), according to the Bible, must remain strictly non-sexual.
Therefore, a good question to ask in place of "can I do this with my girlfriend" is "could I do this with my sister?" (For clarification, the same works when the genders are reversed, it's just that, as a man, I feel more qualified to speak on behalf of my own gender). Can you hug your sister? Sure, so you can hug your girlfriend. Can you hold hands with your sister? Sure. So you can hold hands with your girlfriend. Can you kiss your sister?
Here you actually hit a roadblock, because the significance of kissing is both a cultural and an individual variance. In fact, the Bible itself says to greet one another with a holy kiss (Romans 16:16). But this isn't for everyone. Personally, I have a "touch me and I'll fight you" type attitude when it comes to kissing, so anyone who tries to greet me with a holy kiss will not be able to do so without resistance. Kissing is strictly romantic to me, though not necessarily sexual. I would therefore consider myself somewhat "middle ground" on this.
By contrast, I know that some parents even in my own culture do kiss their children, even on the lips. Sometimes, siblings do it too. To give an example closer to Biblical times, the Greek historian, Herodotus (484 B.C. - 425 B.C.) noted that the Persians would greet those of equal status with a platonic kiss on the lips, whereas they would greet those of lower status with a kiss on the cheek. Compare that to other cultures where kissing is practically unheard of, and even seen disgusting. Which, when you think about it from a scientific standpoint, is perfectly understandable.
So, there are three questions you need to ask when it comes to figuring out whether or not you can kiss your girlfriend. First, what does your culture think about it? Second, what do you think about it? Third, and frankly most important, what does she think about it?
The culture matters for two reasons. First, because it will inevitably affect the answer to the next two questions. You are part of the culture, and so will likely have inherited at least some of their views. Second, because it will affect your witness. If you're in a culture where kissing is seen as offensive, or sexual, then doing so will altar their perspective of your faith. It follows the same principle of not eating meat to avoid causing people to stumble (1 Corinthians 8:13). It's also important to keep up appearances so that God will not be blasphemed (2 Peter 2:1-2).
What you think of it matters, not because I am endorsing a relativistic approach, but because we are supposed to guard our hearts. We are especially supposed to be sober and vigilant against the devil (1 Peter 5:8). He will take any opportunity to tempt you, and so if you are even remotely tempted by kissing, don't do it.
What she thinks of it matters for two reasons. First, you have as much responsibility to protect your girlfriend from temptation as yourself. At the very least, woe betide you if you are the source of her temptation! Second (though I rather hope this goes without saying), you need her consent before you do anything. A woman is a precious thing, and her purpose is not solely to please her man. Rather, she is made in the image of God, and was designed to please Him. Therefore, you should never allow her to feel pressured, and especially not threatened, by you. If kissing is not right for both partners, it is not right for either partner.
A good relationship requires three individuals to be on the same page: God, a man, and a woman. My brethren, God is the one who decides what page you are supposed to be on. Even if you are both on the same page, that page is cursed if it's not where God is. God's page describes three categories:
- Marriage. Most boundaries removed.
- Family. Strictly platonic.
- Friendship. Strictly platonic.
Using the family category as a benchmark, the question of boundaries within a pre-marital romantic relationship is fairly simple. That which you can do with your sibling, or parent, you can do with your partner. That which you can't do with your family, you can only do with your partner if you marry them and it remains moral. Any grey areas can be solved with a fairly simple comparison with the culture, and a thorough, prayerful search of the conscience.