1: if one were to speak of ..., then certainly; if it were the case that ..., then certainly; if it were a ..., then certainly; phrase used to indicate the inevitability of what follows it (based on what precedes it);2: so that means (when used in sentence-initial position)
Hatsukoi to iu to, mazu nani wo omoiukabemasu ka?
When you say "first love", what is the first thing that comes to mind?
You can also use this to refer to your own question:
Doushite akirameta ka to iu to mou gaman dekinatta.
The reason why I gave up is because I couldn't take it anymore.
Lit. If you ask me why I gave up, I couldn't take it anymore.
Reference: Maggie's site