If the boundary is one cannot have a partner who looks at porn, cheats, etc... and that partner conceals what they are doing rather than complying with their partner’s boundary, then that boundary is being crossed and violated, not observed. The fact he is concealing means he is not respecting the boundary, one can safely assume.

So, then you can either loosen your boundary, letting them plow right over it, and accept their behavior or make firmer demands, or end the relationship when that boundary is truly a deal breaker.