The beginning "if" primarily means "if", but it needs a specific form of verb meaning something that "might" or "could" happen. When used with a verb of something actually happening, it means "since”.
The key word "become" is mistranslated as "been". This "being faithful" completed in the past. This misses the point. We "become" faithful over time. We try to become trustworthy over time.
Another key word is translated as "that" and "property”. It can be used as "that" but it never is translated accurately as "property." The word means "something”, so, the "something of another" and "something of your own." It could mean property or simple money.