August, Melania, and Valerie were all undergoing their own trials.
Melania definitely faced something leagues above what the other two were facing, but they were all being challenged in ways that would help them grow.
For Valerie, it was character rather than potential.
Damien truly put her in a situation to test her loyalty. Not to August and Melania, but in general.
He needed to see if she would betray others for her own sake, since she was generally someone who prioritized herself over others.
And, he needed to see if she would be a friend worthy of August.
Regardless of the outcome of her test, he wouldn't interfere in their relationship. If she truly was a person unfit for their group, then August would eventually learn the hard way.
That was a life lesson for him. If Damien interfered, then it would become meaningless.