I've had partners like that, and there are usually two scenarios: either they're genuinely people who struggle to mix their different social circles (some of us are weird like that), or there's something they don't want you to see. The difference is whether the rest of the relationship works well - if he introduces you to his family, includes you in other areas of his life, and it's just his friends who are the exception, it's probably just how he is. But if he generally keeps you separate, avoids talking about the future, or is secretive with his phone, then yeah, it'd make sense to talk to him directly about what's going on, because after almost a year you deserve clarity.