Boyfriend won't answer my question just keeps responding with a question?

So I keep a tight watch on all my boyfriends because I've been cheated on before so I go through their phones when I can and check their search history etc and I noticed lately his instagram search history is empty so I confronted him and asked "why is your instagram search history clear?" and he just responded with "why are you checking my search history?" and I told him that's not the issue here and asked him again and he responded with the same question and won't budge what does this mean and what do I do?

Updates
+1 y
To clarify he's never cheated on me (that I know of) but keeping an eye on his DMs etc is way to make sure he never does.
Boyfriend won't answer my question just keeps responding with a question?
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