This is one of the reasons why the author is amazing... I think they kind of put you into Arvo's perspective so well that you don't really notice how isolated from your friends you've become until it's too late. You get pitted against Lake and against Mikko and against everyone because he wants to test how far you're willing to go for him.
Torulf is kind of toxic because he's driven on a base level by a desire for recognition due to—from my perspective at least—a lack of confidence in his own self worth. He seeks external validation to feel as though he means something. We see this in the way he preens in front of others, and his openly flirtatious attitude. We see this in his actions towards the MC and towards lake.
However his desire for external gratification melds with his fear of commitment and creates this really unhealthy balance of push and pull on people's feelings.
Look at Lake, for example. On the one hand, Torulf desires to be close to him physically and maybe even emotionally in some deep hidden way. He loves the attention and the compliments. He loves to be desired, but when the sex is over, and the cuddling is past... when the gradification ends... he's left empty again, and because he can't fill himself up with his own confidence and his own love, he goes out to seek it from others once again.
This creates a poisonous cycle of distancing himself and getting close and distancing himself and getting close. Hot and cold if you will.
If you haven't yet played Lakes route yet, I would do so. If I'm correct you get a glimpse into Torulfs mind near the end of the newest update. I shall leave it at that. Hopefully my ramblings make sense.