You learn who someone is when supporting you stops benefiting them.

While supporting you also serves someone’s interests, you cannot tell which one is driving. The information arrives at the point where backing you becomes costly or simply pointless for them, and their behaviour then is the answer. This is not a reason for suspicion of everyone. It is a reason to hold your conclusions lightly until the situation has actually tested them.

Think about who stayed when there was nothing in it for them, and value those people accordingly. When someone drifts once you are no longer useful, take it as information rather than betrayal. Both kinds of people are worth being able to identify.