The first few paragraphs of this post sent me in “WTF? Seriously?” mode until I realized that by “rationality” you specifically meant explicit LW-style x-rationality rather than just not being an idiot. But getting kicked in the rationals is no fun, and I already get more than enough of those from people whom I can't choose whether to interact with; so if someone did that on a regular basis I would become much less willing to be friends with them, let alone be their boyfriend. (If I were single I'd have no particularly strong objections to have casual hookups with such people, but that's not incompatible with holding out for a long-term relationship with a non-idiot.)