I was wondering who he really considers to be his trusted friends in his home country but I come up with a very short list of people I assume he trusts:
1. W'Kabi...I don't think it's ever been spelled out but I always assumed this was T'Challa's closest male friend in Wakanda.
3. Taku...I tend to think of W'Kabi, Zuri and Taku as his 3 most closest advisers.
4. His step-mother Ramonda
5. Okoye...and I'm hesitant to add her. I believe he trusts her with his life but not so much with his secrets.
I would add Shuri ( his sister) to the list. At one time I'm sure Ororro was on the list as well. Maybe Steve Rogers. Given his personality and his stature; he doesn't have a large 'inner circle'. That's probably the way it should be. How many monarchs do you know that have a large inner circle.