What the protestant was proposing to you is their “doctrine” of “Once Saved, Always Saved”, (OSAS), which is a new teaching which began fairly early into the so called reformation in the mid 1500s. It is especially held by the followers of John Calvin. I believe it is wishful thinking on their part.
There are lots of threads on the forums all the time, with folks throwing lots of scripture verses around to make their point. The Catholic teaching, based on the totality of the scripture is that once a believer is in a state of sanctifying grace after accepting faith in God through Jesus the Redeemer, (which grace is a free gift of God which we must accept to ever be “saved”), nothing outside you can take you away from that saving faith. The difference between many non-catholic Christians and Catholics is the protestants claim nothing at all, even your own decision to reject your faith in God by committing deliberate serious or mortal sin can take away your “salvation”.
If anyone “cherry picks” their verses of scripture, accepting those they like and believe make their point and ignores the rest, they can come to that conclusion when relying on their own interpretation of those picked verses. The Catholic Church has always taught that we must study issues based on the totality of Scripture, not just on those select few verses we like.
All Christians believe that God is all powerful, and when in relationship with Him through His Son, He provides us the grace we need to resist further sin. Catholics believe that God loves us so much that He doesn’t force us to stay in that relationship, but will reluctantly let us walk away if that is the foolish choice we make.
I hope I have answered your question. Search on the forums for OSAS, and its alias “Eternal Security” and you will find a great deal of disagreement.
God Bless