Since "No one who is born of God will continue to sin, because God’s seed remains in him; he cannot go on sinning, because he has been born of God" 1JOhn 3:9, then there's no possibility of falling away. And that fact is confirmed in the same epistle where John states, "They went out from us, but they did not really belong to us. For if they had belonged to us, they would have remained with us; but their going showed that none of them belonged to us." 1John 2:19 Thus passages such as Romans 8 which speak of there being no condemnation for those in Christ Jesus, are simply describing the behavior of those who have been born of God. This as opposed to the suggestion by you salvation by works Christians who view one's performance as a condition for salvation.
Furthermore the very concept of being born is uni-directional. Having been born a person cannot become "unborn", as you suggest. And as for "in Christ Jesus", it is written:
Eph 1:13 In Him you also trusted, after you heard the word of truth, the gospel of your salvation; in whom also, having believed, you were sealed with the Holy Spirit of promise (Nothing about works) Sealed for eternity, having come to belong to Christ.
You salvation by works Christians put your trust in your own performance to save you, this as opposed to trusting in Christ to save you. And since you don't put your faith in Christ you don't qualify to be saved. One evidence that a person belongs to Christ is that they affirm the gospel of grace. Testifying against the gospel, making salvation out to be a matter of one's performance is evidence to the contrary.
Yes we are forever sealed with the Holy Spirit. It doesn’t say we are sealed with salvation. Do we lose our free will when we receive the Holy Spirit? What did Paul say just 3 chapters later about being sealed with the Holy Spirit? Let’s continue reading together shall we?
“And grieve not the Holy Spirit of God,
in whom ye were sealed unto the day of redemption.
This proves that people who are sealed with the Holy Spirit can still disobey out of their own free will.
Let all bitterness, and wrath, and anger, and clamor, and railing, be put away from you, with all malice: and be ye kind one to another, tenderhearted, forgiving each other, even as God also in Christ forgave you.”
Ephesians 4:30-32 ASV
Let’s continue in Paul’s message with the next chapter.
“Be ye therefore imitators of God, as beloved children; and walk in love, even as Christ also loved you, and gave himself up for us, an offering and a sacrifice to God for an odor of a sweet smell. But fornication, and all uncleanness, or covetousness, let it not even be named among you, as becometh saints; nor filthiness, nor foolish talking, or jesting, which are not befitting: but rather giving of thanks. For
this ye know of a surety, that no fornicator, nor unclean person, nor covetous man, who is an idolater, hath any inheritance in the kingdom of Christ and God. Let no man deceive you with empty words: for because of these things cometh the wrath of God upon the sons of disobedience.”
Ephesians 5:1-6 ASV
Now those who greave the Holy Spirit have no inheritance in the Kingdom and will suffer God’s wrath. Why?
because of these things cometh the wrath of God upon the sons of disobedience.
These people who greave the Holy Spirit are no longer sons of God but yet we see that they were once sons of God and are still sealed with the Holy Spirit. Now they are the sons of disobedience. These people will still forever be convicted of their disobedience by the Holy Spirit because they have received knowledge from Him that they will never forget and will always be called to repentance. However they are never forced to repentance.