Okay, I know it's fairly common with manga translations, but that is not how you use the word since in English. "It's not like I fell in love with him since our first meeting." No. Incorrect.
Since implies a continuation, usually from some point in time continuing on to the present time. "Fell in love" is a specific, complete action that cannot continue to the present. It is not proper to say "I fell in love with him since our first meeting". I fell in love with him AT our first meeting. I fell in love with him DURING our first meeting. Even though during also implies a continuation, the context here would have it end when the first meeting ends, so it would be fine. At or during would be much better translations.
/rant I know it's common, but it's a really annoying mistake. Not trying to offend the translators, though; thank you for the work.