I can't believe that in this era, we still have to talk about this topic. I've heard and seen couples, infact, I've been there before, who mutually agreed not to kiss until marriage. It wasn't until recently that I realized that some actually practice this because they believed it was a sin.
For me, and I think for many others, I did it because I felt it was something I would like to reserve for the wedding day? Kinda like something to look forward to? Never did I once thought that it was a sin. So coming across that belief took me aback and I had to find out exactly why they felt it was a sin.
The notion was simply that, when you kiss someone, you lust after them and you think about having sex with them. Of course we all know that famous quote by our Lord, Jesus Christ in Matt 5:27-28 "anyone who looks at a woman lustfully has already committed adultery with her in his heart" so based on that notion, kissing is a sin.
Now I'll like to think that such thinking is quite shallow-minded unfortunately, because, there are so many reasons people kiss that doesn't lead to lustful thinking. So many, and it's seriously worrying that some group of believers have concluded that every form of kissing leads to lustful thinking so therefore it's wrong and should not be practiced unless one is married.
Like I said there are so many reasons why people kiss. Eg. People kiss to show appreciation. People kiss as a form of greeting. People kiss to say goodbye. People kiss to affirm a stance. People kiss to say I love you. And then there are times that people kiss because they want to have sex. So we can't simply conclude that all kissing is wrong. That's stereotypical and prejudicial. It's like seeing guys playing a game of cards and concluding that they are gambling because cards are predominantly used in gambling games. That's not right.
But inasmuch as kissing maybe ok, I wouldn't suggest it for weak couples. I won't suggest you do it behind closed doors. I wouldn't suggest you do it if you can't control your sexual desires. Like Brother Paul said, everything is lawful for me but not everything is helpful. 1st Corinthians 10:23. Cut your coat according to your size. If kissing makes you lust and get all excited, then maybe you should abstain from doing that till you are matured enough to handle it. To you, kissing will be a sin if you engage in it, but that doesn't mean everyone else doing it is committing a sin.