Did Simon admit
 

a) he'd be willing to cheat on his bf
b) he'd not been satisfied in sixteen years?!

I don't know if it was what he meant, but from Simon and Eileens conversation, I gathered that after 16 years the sex was a bit unadventerous with his boyfriend and he was feeling lust for Marc. That was why Eileen said 'It wouldn't be worth it', even if Marc were gay.

The whole convo was a mess

Eileen disappointed me bigtime tonight in all her chats with Simon.