How does one know if they are being faithful to Jesus, and at what moment can one know they are not?
Consider the following passage...
“My son, do not despise the chastening of the LORD,
Nor be discouraged when you are rebuked by Him;
6 For whom the LORD loves He chastens,
And scourges every son whom He receives.”
7 If you endure chastening, God deals with you as with sons; for what son is there whom a father does not chasten? 8 But if you are without chastening, of which all have become partakers, then you are illegitimate and not sons. 9 Furthermore, we have had human fathers who corrected us, and we paid them respect. Shall we not much more readily be in subjection to the Father of spirits and live? 10 For they indeed for a few days chastened us as seemed best to them, but He for our profit, that we may be partakers of His holiness. 11 Now no chastening seems to be joyful for the present, but painful; nevertheless, afterward it yields the peaceable fruit of righteousness to those who have been trained by it. (Heb 12:5–11)
The first two things to consider are 1) that the Lord chastens every person that is His child when they go astray, and 2) only those who are not His children do not partake of His correction (double negative, I know). So, at the very moment you experience His correction you can know for sure that you are going astray.
The other thing to consider is that when He has trained you by His correction (which is painful), the painfulness of the correction is replaced with peace with God. So, when the pain stops and the peace ensues, you know you are being faithful to Jesus.
Does this give you the sense of direction that you are looking for?