"Could The Lord really have changed him? Granted that it's only been several months since his last relapse, could him getting closer to The Lord prevent him from another relapse? Is that possible? "
yes, but it involves more than that.
faith without works is dead.
Thus also faith by itself, if it does not have works, is dead.
Show me your faith without your works, and I will show you my faith by my works.
You see then that a man is justified by works, and not by faith only.