SHORT ANSWER: Sometimes yes, sometimes no, depending on whether the activity leads to lustful thoughts and desires.
LONG ANSWER: The Bible doesn't say anything directly about kissing or making out. (The Bible also doesn't talk about holding hands, video chatting, or eating frozen yogurt together.) So, in situations like this (and many others), my general advice is to find out what the Bible does say about similar stuff and see how it relates to the topic at hand.
Sexual Sin and Lust
While the Bible doesn't mention making out, it does speak VERY CLEARLY about sexual sin. We are to avoid it (1 Thessalonians 4:3) and even flee from it (1 Corinthians 6:18-20). But what exactly is sexual sin? Some things are clear in the Bible, such as sex outside of marriage (fornication), sex with a person who isn't your spouse (adultery), or sex with a person of the same gender (homosexuality).
But what about all the other stuff that two people can do together? Believe it or not, Jesus answered this question without even having to list them all out. In Matthew 5:27-28, he says "You have heard that it was said, 'You shall not commit adultery.' But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart."
Simply put, if it leads you to lust, then it's sin.
So then, what is lust? It simply means to want, to desire, or to crave. The Greek word used here is defined as "to strongly desire to have what belongs to someone else and/or to engage in an activity which is morally wrong."
This is the same for guys and girls. Don't think for a moment that only guys lust. Girls can want, desire, and crave just as much as guys, although it usually looks different for them.
What About Kissing?
If kissing somebody makes you want more, then it's probably sin. If it makes you want something that "belongs to someone else", like her butt or his abs, then it's definitely sin. And if it makes you want to "engage in an activity which is morally wrong", like having sex, then it's definitely definitely sin.
It is possible to kiss somebody without lusting (like kissing your mom or giving someone a thank you peck on the cheek), but I think it gets more risky when it's somebody you're really into. Also, because lust is in the heart and mind, it's possible to start lusting long before lips touch and continue lusting long after the make out session is over.
What About Making Out?
Making out can mean a lot of different things, but most people seem to agree that it usually goes beyond simply kissing lips. So, here are some general guidelines about what sinful making out looks life:
- There's skin-on-skin contact
- It involves fondling sexual body parts (like butts, boobs, etc.)
- It involves body parts that are particularly sensitive to getting turned on (like the neck, ears, abdomen, lower back, etc.)
I think any of these activities would lead a person to want or desire more, and once you've crossed that line then it's lust, which means it's sexual sin.
Remember, the issue isn't kissing or making out; the issue is lust. So, don't ask "Is it okay to kiss?" but ask yourself "When do I start lusting?" And then stop before you get there.