asking for advice. only 18+

my friend has a girlfriend who met on tinder abroad and they started seeing each other as she came to our country. (i haven't heard from him for a while because i was focused on my studies, so I don't actually know if they're still together, i hope not) The issue is that she lied to my friend on being 19 the whole time she was with him, and she actually was 3 years younger than him. He didn't know that and still had s&x with her a few times. During her stay in my country she was still 16 (he wasn't aware) and my friend had just become like 20 a week ago, she would have become 17 a month later. My friend discovered it during her stay, and i'm afraid about the possibility that he could have had s&x even after discovering the age, because maybe he could have thought that he had just become 20 and that she was basically 17, while on paper until that following month she would have been 16. My friend is a good guy, I do not know how to ask this without sounding weird. I asked advice before and some people think he's a creep and deverses to be arrested. He's not that type of person I can assure you that. I think it mainly lies on ignorance and stupidy rather than malice, since, while not personally agreeing with it, a 3 years age gap in my country is considered not weird, even though i find it personally inappropriate. I will try to confront him about such topic, and make him realise it's inappropriate. I don't know what should I actually do. I don't want to break that 10 years friendship. Wouldn't a good friend be someone who made him understand and make sure they don't repeat it again instead of cutting them off their life completely? And to what degree is something forgivable or not acceptable? If he still kept the relationship and put on hold any se^ual rapport, after gaining the age gap context, but was unsure if to still try to keep the romantical relationship as he catched feelings (they've been in a 1 year distant relationship), and then came to his sense and break it off, would i be still allowed to be his friend? and what if the worse happened? not thinking deeply abt it and generalising the fact that they were basically 17 and 20 and kept having s&xual rapports? I don't know what could I do in such case. I really hope he didn't. I'll talk to him about it. But please offer any help.