A lot of the relationships trigger based on the number of points in the LIs path and most have some have *critical* moments that you'll want to do. If you don't want to enter a specific relationship, don't excessively flirt or choose more romantic choices, such as kissing. It's pretty easy, just balance flirtier options with neutral options. That'll let you selectively choose/avoid relationships.... if you want some assistance try the Walkthrough PDF, or if you are comfortable with the risks of modding Scrappy's mod on the OP that has built-in guides for choices.Actually, no, it was that the choice was made for me. It was a pop up dialogue that said I had to choose. Knowing now that this isn't a harem-type game, that now makes some sense.
And yes, some combinations of relationships already have some pretty heated/fiery moments.