Is what I did, in trying to distance my colleague from a Christian man, correct, and what should I do if I discover that I love her after that?

In summary, there is no permissible love relationship between a young man and a foreign (non-mahram (definition)) woman except through marriage. Any interaction that arises between them outside the framework of marriage is often due to impermissible mixing, which leads to forbidden acts. A person cannot protect himself from falling into the forbidden except by marriage for those who are able, or by fasting for those who are not able, because true love is only born after marriage. As for enjoining good and forbidding evil, it must be done with Islamic guidelines, including: that the evil must be known, that forbidding it does not lead to a greater evil, and that one does not expose oneself to temptation.