Question:I truly loved a girl. We had sex. We made a kissing picture and I put that picture on a web site. That was my mistake. Is that a wrong thing to do?
I hope I understand your question accurately. If I misunderstood, please help me to understand better so I can help you.
I notice that you are writing in the past tense. I assume that you loved a girl but no longer. I take it that she got upset because you posted a picture that she found embarrassing. You call it a "kissing picture," but I suspect there is much more about this picture if it led to an argument and break up.
I know you claim to have loved her, but it is clear that isn't the case. If you were in love with anything it was your own pleasure. Is it love when a guy puts up a picture of his girlfriend for all the world to see, a picture that embarrasses her? Who benefited from that showing off? It certainly wasn't her. So, I must conclude that the picture was posted to give yourself a chance to brag about the girl you were doing. And you call that love?
Paul tells us in I Corinthians 13:4-8 that love is kind, yet you acted unkindly toward her. He said love doesn't behave rudely, yet you embarrassed her. He said love doesn't brag or is arrogant, yet you want the world to see your sexual exploits. Though true love never fails, your love is past, but that is because you didn't love this girl. You loved what you got from this girl.
The damage you caused is not just to the girl or her reputation; you damaged yourself as well. "Flee sexual immorality. Every sin that a man does is outside the body, but he who commits sexual immorality sins against his own body" (I Corinthians 6:18). While you remain in this sin, you keep God out of your life. "Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God" (I Corinthians 6:9-10). Fornication is having sex with someone to whom you are not married.
Was it wrong? It sounds like the whole relationship was wrong because you wallowed in sin. My question to you is what are you going to do about your sin? You can't improve your life until you first improve your relationship with God.