Ooh this is interesting! I've thought a bit about it being one or the other but never both at once 🤔
I think there are a few ways it could go, tbh:
1. They each assume the other is very experienced & try to hide their anxiety, fumble around a bit trying to seem experienced, & are carried along by their insane chemistry. They confess the truth in the morning & die of laughter/embarrassment when they realize they could've just admitted it. The next month is spent experimenting & becoming very, very good at getting each other off lmao
2. Somehow they actually manage to talk about this/realize they both haven't had sex before, & take things slow over a week or so. They're both awkward at first, but Lyney is extremely tense & unwilling to say what he already knows he likes/wants to try, & Wriothesley starts to wonder if maybe he's just not someone who enjoys sex.
Ultimately he realizes that Lyney just has a really scary, trauma-related understanding of what intimacy is in general, so he does something radically different from what little experience Lyney does have (spending an hour just touching him & not expecting anything in return maybe?). I could see a service top being awakened when Wriothesley's protective instincts kick in to try & make Lyney comfortable...maybe he comes untouched the first time he actually gets Lyney off...
I feel like I'm gonna end up having a lot more thoughts about this now that you've brought it up tbh