1. the bible says that if you repent all sins are forgiven right?
It says that justification is by faith.
What does that mean? It's like, imagine that every time you sin, it goes down on a criminal record.
Sin is any violation of that principle taught by Christ, love God and neighbour as oneself. So, have you ever failed to keep it by, I dunno, cursing or hating someone or blaspheming or whatever? Of course you have. If God judges you by this record, you will be declared guilty and subsequently punished: hell. By default this would mean everyone ends up going to hell, because everyone has sinned at least once in their lifetimes.
The solution to this dilemma is that
Jesus acts as a kind of representative on your behalf who never sins, yet as your representative takes punishment for your sin while you get credited his obedience to God. In this way you can be declared just instead of guilty. It's salvation-by-proxy, basically.
Now, who does that solution apply to? Not everyone; not everyone believes in Jesus, not everyone is going to heaven. However, some people when they learn about this way of salvation, they have a change of heart, they repent, they start moving in a different direction in their life, and they trust Jesus' righteousness credited to them to make themselves good with God rather than their own. That's the kind of person who gets forgiven. Not someone who's good enough, but someone whose saviour is good enough and has had a change of heart.
it also says that if you have sex or anything like sex before marriage you will not enter the kingdom of heaven.
It does not say that if you have sex, or even premarital sex, that you will not go to heaven.
It does say that those who are sexually immoral will not go to heaven.
What is sexual immorality? In principle, it is any way in which you fail to love God and neighbour as oneself with your sexuality. Obviously rape would count, but God also takes issue with other things like homosexuality and prostitution and so on.
People who are repentant yet struggling to maintain sexually pure are not dirty; they are simply struggling to show their true nature: a person who is clean. There's a world of difference between, say, a gay "Christian" who is proud and unrepentant of their sin, and a person who has like an addiction they are trying to get over.
While the Bible does not explicitly spell out every form of sexual immorality conceivable, it is explicitly pro-heterosexual marriage, so that is what should be done. Keep your sexuality in your marriage, and keep your sex life guided by the golden rule.
or even if you have unclean thoughts or lust after a woman before marriage or a marrid woman you will not enter. so. being a guy and human. ive already had sex before marriage and doen other things. i feel guilty about them yes and i have repented and i try incredibly hard to not do these things. but if i have already done them then i cannot eneter the kingdom of heaven right? so what would be the point it not doing it anymore?
Salvation-by-proxy.
There is no threshold or scale or whatever with regards to how much sin you can get away with. It doesn't work that way.
One sin is all it takes to be guilty before God and get yourself in hell.
So, that taken by itself, it's game over for everyone.
The solution, as I said before, is Christ's obedience to God being credited to you inspite of you, rather than your ability to be good enough for God.
Will you trust that, rather than your obvious history of guilt and failure to be good enough? Do you want to live a Christian life? Then you are a Christian and not going to hell.
Romans 7:22-25
For I delight in the law of God, in my inner being, but I see in my members another law waging war against the law of my mind and making me captive to the law of sin that dwells in my members. Wretched man that I am! Who will deliver me from this body of death? Thanks be to God through Jesus Christ our Lord! So then, I myself serve the law of God with my mind, but with my flesh I serve the law of sin.
If you can identify with St Paul's statement there, you're a Christian.