And you need to study and reflect on 2 Tim 2:15 “Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth.”
I would caution you not to diminish the finished work of Christ. We will pray for you.
As for Romans 8, I know the chapter intimately. It is hands down far and away the greatest chapter in the entire Bible. Verse 9 says that we are positionally perfect. Verses 18-22 reveal God's purpose behind salvation. Verses 31-39 reveal the love of God. And verse 37 tells us who we are.
Yet it is very possible for us to walk away from this. Paul warns us against grieving the Holy Spirit by whom we were sealed for the day of redemption. Because if we do, we may find ourselves subject to the consequence of the unforgivable sin and one that we would not have confessed much less repented for when that day of redemption comes.
I get the point about God's infallibility. But we as humans are fully capable of forfeiting a gift we had at one time accepted. As for 2 Timothy 2:15, my translation begins with 'be diligent'. If OSAS is true, there would be no need for being diligent. In fact, all of 2 Timothy 2 would be a waste since there is no legitimate reason for godliness once a person gets saved. In fact, one could discard the entire New Testament save for a few verses if it was impossible to forfeit salvation. Jesus entire gospel of the kingdom of heaven would be pointless as well since the kingdom represents the restoration of our souls (among other things) after our spirit has been renewed. Yet the OSAS doctrine gives no account of the process we endure after we accept Christ and His Spirit as a foundation for living.
And in no way am I diminishing anything concerning the finished work of Christ. But I would remind you that Covenant is a two-way street. If the finished work of Christ was all it took, then everyone would already be saved.
I will leave you with this: