I believe sin separates us from God.
The Bible tells us differently.
Romans 8:35 - 35 Who shall separate us from the love of Christ? Shall trouble or hardship or persecution or famine or nakedness or danger or sword?
The answer is No one. More than that, Paul lists all the things that WON'T separate us from Christ's love.
38 For I am convinced that neither death nor life, neither angels nor demons,
neither the present nor the future, nor any powers,
39 neither height nor depth, nor anything else in all creation, will be able to separate us from the love of God that is in Christ Jesus our Lord.
The bolded words include EVERYTHING that can happen in the present or the future. That would include sin.
Even sin can't separate us. Why? Because Christ died for sin. It's no longer an issue in salvation.
God doesn’t separate me from him, my sin that I freely choose does.
For the believer, you are correct. Your sin will separate you from fellowship with God. That is why John gave us 1 Jn 1:9, so we can be restored to fellowship through confession of our sins.
If I choose to commit adultery against my wife, 1 Corinthians says I will not inherit the kingdom of God.
It is a mistake to assume "not inheriting the kingdom" means "not entering the kingdom". It doesn't, regardless of what your pastor may say.
To "inherit the kingdom" is the same as saying "reign with Him".
2 Tim 2:12 - if we endure, we will also reign with him. If we deny him, he will also deny us;
Some translations have "disown", but if that were the meaning, then that verse is contradictory with Romans 8:35. And Paul wrote both of them.
What Christ will deny us is the privilege of reigning with Him.
Same teaching in Romans 8:17b- co-heirs with Christ, if indeed we share in his sufferings in order that we may also share in his glory.
iow, in order to "share in His glory" which means the same as "to reign with Him" in 2 Tim 2:12, we have to "share in His sufferings", which means we have to "endure".
At the moment I decided to do that, I turned my back on God and what he expects from Christians. He still loves me and wants me to be saved, but he will not reward me with heaven unless I make that right and confess my sin.
No, once you have been given eternal life, which occurs AT THE MOMENT of saving faith in Him, per John 5:24, Jesus says recipients of erternal life shall never perish, in John 10:28.
Do you believe what Jesus teaches?