There is more than one way to be out.
Maybe he just doesn't want his family and friends to know but he’d be ok with yours knowing, or maybe you decide on a mutual third group of people who you have in common that he feels comfortable sharing that information with and wouldn't feel judged. Even if that’s not possible, consider that for him, just being with you, might be his way of being out!
Your relationship is valid.
Ok, so you can't post his pic everywhere, your friends don’t know him (and that's probably a good thing!) and you may not know his family, but who knows, he might be sparing you! In any case, it doesn't mean that you aren't a real couple. If you're with him and he's with you, you’re together — and that's called a couple!
You are not alone.
Men keep their relationships to themselves for various reasons. Sometimes it's because, they know that it would ruin their relationship with their family or because it’s not safe for them. Sometimes they are just scared. You are not the first person to have someone in your life who you love that is not as open, as loud or as proud as you are, and just because they aren’t doesn’t necessarily mean you should give up on them.