He may not be as "loyal" to some other characters as he is to Ian, and I've known a person like Jeremy irl. Sometimes the way he treats other made me scratch my head but he always treats me well and we've been friends for 7 years. And in ORS, I play as Ian and I look things through Ian's perspective only (to be realistic as irl) and ignoring his shenanigas to others.As has been said, it's not a popular opinion here but some people do think he is. I think he is, as far as his personality and perspective go. He's not the sharpest tool in the shed, but he is loyal, he doesn't spill the beans to anyone if he sees Ian and Cindy together, and if Ian is sleeping with Alison and/or Emma he's excited to have sex with them too but isn't trying to go behind Ian's back or "steal" them away from him. His enthusiasm about being eskimo brothers may be immature, but it's also sincere.
Chapter 11 did add a potential complication, in that Jeremy didn't tell Ian about seeing Gillian with her boyfriend at Blazer, and when Ian confronts him about it, Jeremy is evasive and vague. That could be something sinister, but also could simply be that Jeremy knows that Ian would be upset if he knew Gillian was back in Baluart, and Jeremy's trying to shield him from the pain by not telling him. Again, it may not be the smartest choice, but it's possible Jeremy is just trying to be a good friend the best way he knows how. I'm guessing we'll find out in future chapters...
The Gillian topic I am leaning to agree with Jeremy. Ian has good things going out with his life. Dating Alison/Cindy/Holly/Lena, get another job, book contest, fighting contest. Why would Jeremy distract Ian with bad memories? I'm sure majority people will do what Jeremy did by not telling his friend's ex doing while they were trying to move on.