To make the long story short, my girlfriend and I were both Christians and we did sex, almost thrice every week. But now I feel guilty and convicted that we should stop doing fornication.
Due to this sin, I think I lost my love and feelings for her and I think I'm longing for my ex-girlfriend who is also a Christian, and my girlfriend's ex-best friend. I want my ex-girlfriend back. Honestly, I think I just used my current girlfriend for sexual satisfaction. I loved her. We were both virgins before and now we are ruined. It's all because of me.
The question is: Should I leave her knowing that I really don't love her? Or should I take responsibility for what has happened to us? We've been in a bumpy relationship because we argue a lot.
Help me. Thanks.
The problem is that you are making decisions emotionally, based on your physical desires, and not rationally. You liked the current girl you are with because she willingly let you use her for sex, but now that the novelty is wearing off, you are starting to see her for the person she truly is and that doesn't make you happy. I suspect that your desire to go back to your first girlfriend is also an emotional response to the situation. You want to go back to a time when your relationships were more innocent and not complicated by sex.
In a lot of ways, you are still not thinking like a grown Christian man ought to think. For example, in everything you've discussed so far with me, it is presented as if the decision who you are with is yours alone to make. You do get to choose who you want to be with, but you need to realize the girls also make their own choices as well. There is only a relationship if the boy and girl come to the same decision.
Yes, you are responsible for who you have sex with. You have control over what you do with your body. You haven't been using it responsibly. If you have gotten this girl pregnant, then it is your responsibility to care for the child that you produced. You are also responsible for the sins that you committed before God. It doesn't matter that your girlfriend was willing. You chose to sin with her. "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).
If I may, let me suggest that instead of bouncing around in emotional decisions that you stop the dating business for a bit until you learn to control your sexual desires better. "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). When you are calmer and not thinking about any particular girl, I would like you to sit down and make a list of all the things you would love to have in a wife. That list should have no physical characteristics. It should be about her personality and the things she likes and dislikes. I want you to do the list when you don't have a particular girl in mind so that the list is more honest.
Then, when you meet a girl, I want you to use your list to decide if this girl is the type of girl you could see as your life's companion. You won't be able to tell immediately, it is going to take getting to know a girl well to see all of her qualities. If a girl doesn't meet your desires, then move on, but under no circumstances are you to use a girl for sex. It isn't fair to the girl or you and it will only skew your thinking to the present instead of the future. I don't know how old you are, but if you aren't ready to think about getting married in a few years, then you are ready for a relationship yet.
Neither you nor your girlfriend is ruined. You've lost your innocence in regard to sex. You've been involved in things that should have waited until marriage. Those things can't be undone. But you can change your future. "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. And such were some of you. But you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus and by the Spirit of our God" (I Corinthians 6:9-11). You can stop being an animal and start being godly.