I'm of two minds about this...the horny, cockcentric 'me' is wondering if you've felt sexually aroused and gotten hard from having been asked to showoff your cock for another dude and visa versa...??
The more level-headed gentleman 'me' is just fkn smiling, especially after reading NIMBUS post above...in fact, he'a spot-on. I suggest reflecting on your own needs (motivations, intentions, etc) before revisiting the invitation. Prioritize the 'friendship' in proactively, with actions, not just words and clarify expectations concerning privacy.
Really, your mate's taken a huge risk so just be mindful not to leave him 'hangin', so to speak, by 'pretending' he hadn't asked, etc...and always reserve the right to change your mind ,tho, hope like hell u give it a go