Loyalty is a finicky thing in this day and age. But I don't doubt true friendships have ever been easy. Seneca invites us to ponder what it means to have true friends and even criticizes his own for speaking ill of a supposed friend. Truly, friendships should act as an extension of oneself — something grown, not given.
Now, time does play a major role in this but we all have friends closer to us than even the longest companions. For myself, I am lucky to say I have a handful of incredible individuals that I trust. And yes, I have passed judgement on them. They have most assuredly done the same to me — otherwise the whole friend thing wouldn't really work. But we all know those people with many friends but none true and vice-versa. So I agree with Seneca, it's not as simple as a personality type of introvert vs. extrovert or I trust everyone vs. I trust no one. Seneca even states there is much danger in this line of thought. It exposes an individual's true issue of not being able to deal with themselves, to use Seneca's phrase, "...they see darkly by day".
Friendships shouldn't necessarily come easy nor do they have to be difficult. A bond is formed through two phases of action: trust and judgement. Now, the tricky part is forming loyalty. I disagree when Seneca states that all it takes is to "regard" a friend as loyal. Does betrayal ever happen expectedly? I would argue it takes a constant effort — just like any relationship. But undoubtedly the simple truth Seneca argues remains — when the two initial phases are over and you regard that person as true friend, confide in them like you would confide in yoursellf.