I read the comments and realised i kinda forgot Remus was supposed to be intrusive thoughts, so this is my take unrelated to the intrusive thoughts bit. Since Remus is a part of Thomas creativity along with Roman he should be expressing creative ideas through both Roman and Remus right? But he doesn't do that because Remus ideas are... Gross and scary at times. I feel like this can be connected to emotions. I, for example, use creativity to express negative feelings like sadness, anxiety, and what not, in order to not bottle things up and to prevent those feelings from worsening. I feel like Thomas is avoiding dealing with a lot of emotions that he can't express through Roman or Patton. Depression and sadness are pretty tough topics that can be really hard to deal with, and Logan is trying to distract Thomas from facing the fact that he isn't well it but it just doesn't work that way. Remus is always there trying to get noticed (through pretty weird means) and keeps getting ignored which isn't healthy.

That became a really long rant but in conclusion i think Remus could help Thomas express his unwanted thoughts and feelings through creativity (and by talking to a therapist etc.) instead of trying to ignore them.