It's ch. 7, this is about as close to the start as you can get to establish a premise.
Them highlighting the phrase "I Love You" for several chapter prior, learning about what love is from his mother, and ending this chapter with him replying "Me Too" like some grand revelation made it pretty obvious this story is going to be about him coming to learn more about love, at least to me.
Ch.0 also showed him thinking about a girl (who I assume would be the love interest), so I don't know what to tell you.