Bad influences

Hello, our teenage son is mostly agreeable when he's with us at home, but he's been hanging out with this one love interest for a couple of months and when he comes back from that he's flustered and angry at us and our rules. We've overheard some conversations where this person is telling our child things like "why do you have such an early curfew, you should be allowed to be out later" and similar things, so we're thinking this person is egging our child on and turning him against us. We've had several counseling sessions with him and he's been trying to do better, but we see this person is still sparking rebellion towards our rules. We're really trying to not just prohibit our child from seeing this person so we're wondering if there's anything else we could do.