James 5 v 16 says: 'Confess your sins to each other', a command which a lot of evangelicals tend to ignore.

The reality of sexual experience amongst kids is that it is common and sometimes very damaging - I recognise a somewhat similar experience in my own life at that age of moving from a desire from older boys to younger following early sexualisation... I suspect we need to see it as damaging in the same way as we see drug abuse as damaging; the fact that it is pleasant at the time doesn't remove the long term consequences. Which is why it was still abuse when the older cousin took advantage of you, despite the fact that you were very willing; we still blame the drug dealer more than the addict.

It's not clear from what you say whether he's been prosecuted for what he did with you; if he hasn't you need to think hard about how to prevent his doing anything more with other boys who might be less able to cope.