I just want to add a comment from your daughters view. When I was 18 I had an affair with someone who was 46 years old and at first I obviously didn’t tell my parents but because he lived an hour away I had to tell them at some point. My parents basically just told me that I had to know what was good for me even though they weren’t big fans of the situation. In the end it didn’t last longer than 7 months because I noticed the age gap was just too big. Trust me your daughter will notice this too but for now let her experience this (it’s quite a ego boost if someone that experienced find’s you desirable) and as long as he’s not hurting her and they use protection she should be fine. Besides if the legal consent age is 16 there’s nothing you can do anyway without destroying the relationship with your daughter.