Metafriending

[Ikarrus]

Yes.

You're just not allowed to go out of your way under exceptional circumstanes (e.g. He's a traitor, you're not) to help your friend you wouldn't otherwise. No OOC communication as well.

If you're teaching him how to play that's also fine.

Also it may be wise to let admins know about you and your friend just in case so there aren't any unexpected misunderstandings.