Straight couples have little discussion required about who's doing what to whom. There's an emphatic 'this is how it plays, homey' about who's putting what in where; if you want to vary from that (and good on you if you do!), there's discussion to be had. But most people won't vary.
Gay couples? It's a negotiation every night. Maybe I don't feel like giving head tonight. Maybe I just don't want to fuck your ass senseless tomorrow night. Is that something wrong with you? no. Might it take a good bit of coercing to get that across? yes.
Chripes, no wonder a lot of older gay men seem so lonely.