KTJ90220

I have a friend who is also positive who I have sex with a few times a month. I exclusively have sex with him but he has a couple other partners who are also exclusive with him. He says the only time he breaks out is when he has sex with me. Could this be because of me or because he has multiple partners? We've had this arrangement for 9 years or so and he says its only when him and I have unprotected sex that he breaks out.