My best friends? Definitely.
Same, +1, I am surprised by these responses. I am actually an extremely private person (e.g. hate all social media), but I discuss everything with my best friends, these are people who have known me for decades from college days. We're talking about 3-4 people. Intimacy is whole point of lifelong friendships. I'm OK with DH doing the same. Although it is a little embarrassing, in some way I almost think it would be a good thing if he does: it is important to have someone to talk things out with, and provided the friend is also discreet and a "friend of the marriage," I think it is more likely than not helpful.