I'm looking for a fic where, because Reid is going undercover, Rossi has to teach him about sex. Hotch is in love with Reid (and knows that Reid reciprocates) but is unwilling to pursue anything, which is why he basically hands him to Rossi. Reid and Rossi develop a relationship, although Rossi can tell that Reid still has feelings for Hotch. The undercover thing doesn't go as expected, but Reid is a total BAMF (and I think he plays poker?), although he might or might not re-injure his knee while fighting the UNSUB. 'Things' eventually happen between Reid and Hotch (read: sex), and either there's a promise of Rossi/Reid/Hotch or it happens in the last chapter, I can't really remember.
Ring any bells?
Ring any bells?