I would only see it as a red flag if he acted like he didn't want you to come see him.
Then I would wonder what he was hiding.
Do you have any reason to think that he does not want you to come see him?

Does he say you can't go to his place, have you ever mentioned going to his place? I wouldn't necessarily see it as a red flag but I would ask him about it.

He apparently lives iwth his sister and family, so i guess there is no place to stay overnight you know like by me because i live alone. But he recently did mention about hanging out with his friends so i dont know...

Are you guys dating seriously?Or just seeing each other (or friends with benefits). Have you BOTH made clear that you are in a monogamous relationship? If you guys are dating and its been a few months now, i think it should be okay for him to introduce you to his family/sister even if he is living with them. No need of an overnight stay, but at least a visit/dinner is not wrong. Has he shown pictures of his place, and his family with him there? You say its been a few months, and you are still not sure who he lives with. I think it's a red flag. Ask him when he plans to introduce you to his family so you can visit him too. See how he responds.

I would clear the situation up and say you would like to come visit him at his place sometime soon and see what he says. My cousin, who when she was dating her now ex husband, he would say he liked staying at her place all the time and that he didn't want to be around his roommate. Turns out he never had a place to stay as he moved in with her. Just ask questions. I can understand if he lives with his family as it may not be as comfortable but I would go there next time to see if what he is saying is actually true. Not that this is the case, but you don't want to get involved if someone is living with an ex or spouse, etc. You just never know.

Have you asked him if you can go to his place. If he objects, I would see it as a red flag.

"He apparently lives iwth his sister and family".

If he's telling the truth there, that's the problem. He's got no place for you two to "shack up" (with all the associated moaning and screaming). No red flag there.

I'm a little confused: Does HE not want you to come down to him, or do YOU not want to come down to him? If HE, ask him about it. If YOU, it's only a red flag if YOU'RE MAKING IT a red flag.

It's only a red flag if there is a secret kept. Better find out if you want a real, long-lasting, loving relationship with this guy. Or just enjoy the friends with benefit status. It can't last forever!

I get the feeling that your intuition is giving you a nudge. Maybe there is something subtle that makes you wonder if he's married? Is that your fear? It is important to listen to those subtle messages and do what you need to do to eliminate that fear or find out the truth.
Peace of mind is worth everything.

From my experience, I have learned to trust my gut instinct on things. At the same time, don't just sit there and wonder. You need to find out if he is truly hiding something. Have you both 'defined' what your relationship is? I agree with others who have said that if he has said he doesn't want you to come see him, then yes, that is a potential red flag.