In terms of yandere archetypes, I feel like Follo also falls into the category of the obsessive, lovesick puppy but compared to Zanka, he's a lot more volatile.
Despite the development in the manga (which for now, only showcased one singular instance of him reflecting), he is a much more emotional, reactive type of person. I think when you don't give him the attention or love he wants from you, he becomes noticeably negative about it.
Emotional outbursts aren't a rarity with him and neither are negative emotions, which he absolutely does voice.
It's a bit of a rinse and repeat with yandere Follo, where he will blame you and then turn around and wince at his outbursts, before seeking you out to apologize. He is very honest and tells you that it's out of love and that he's struggling, so that you'll forgive him. You always do