Daughter dating a guy who groomed her what would you do?

My daughter was 15 at the time and a Girl Scout. A younger leader (18) took a liking to her and they were sneaking about on camps etc. I found out and put a stop to it. It’s actually illegal in my country under the sexual offences act.

She’s now 17 and he’s 20 and it’s legal and she’s just confessed to seeing him all a long. I absolutely hate the guy. I’m wondering should I play it cool pretend to be ok, be nice to him in the hope she will get bored and dump him?
Daughter dating a guy who groomed her what would you do?
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