Harry is suspicious as hell in Peace Talks. He’s lying to everyone, and not very well. Carlos had every right to be suspicious, because Harry was acting suspicious, and Carlos still came to him as a friend first. Carlos even voted to keep Harry on the White Council, despite the fact that Harry was being incredibly suspicious.

People put a lot of emphasis on Harry being friends with the Knights Of The Cross, but 99% of the White Council doesn’t know Michael Carpenter. Carlos can think Michael is a good guy but that doesn’t mean Harry isn’t lying and keeping secrets. Hell Carlos thinks Harry is a good guy, as evidenced by everything he’s done up to and including Peace Talks, and the fist bump after the cemetery in Battle Ground. But Harry keeps lying to Carlos and isolating himself, until he stops looking shady and starts looking guilty. And even then, Carlos comes to tell Harry that he’s been kicked off the White Council for breaking the first law of magic and killing human servitors. That’s not even Carlos breaking Harry’s trust, that’s Harry breaking the first law of magic - a death sentence - and then being excommunicated for it. Harry burned the Carlos friendship bridge as often as he could in PT and yeah, he damn sure should’ve trusted Carlos. Or at least been less shady.