There are over 100 quests in Grunge, but it is NOT necessary to complete all of the quests in order to get the romantic ending. 

If I was a cooler, more talented dev, I could have made some sort of secret special ending that you get after achieving ALL the quests, but alas, this is my first game, and I am incapable of such a feat.

Endings are determined on the number of heart tokens that you have when you reach the end of the game. 

32 or less - you end up with the alone ending. 

33 to 80 - you end up with the just friends ending. 

81 or more - you end up with the romantic ending. 

The Alone ending and Just Friends ending have special surprises if you play the game a certain way. I don’t want to give it away completely, but certain choices you make in Chapter Two add another event to your ending. 

So I guess that means that there’s really more like… five different endings, if you take that into account.