During my mass effect 3 playthrough I saved Kaiden back in ME1 and I always thought of him as a great teammate and friend but then out no where my conversation with Kaiden became romantic like he wanted me to be more than just "friends" or a "comrade" but I declined him so I could stay loyal to Liara's love. But after that moment I just went back looking to normal and Kaiden and I were still warbuddies. Kaiden,James and Shepard made a great trio(each one different and brought some different to the table but also fighting for the same goal. I told James to become a Specter. And Kaiden seemed like a great biotic teacher and solider who kicked a lot ass)
Maybe on my next playthrough with my other Shepard I might use him as a teammate but as a lover I don't see him like just like with Garrus and James. While if I play Dragon Age II again I'm gonna have same sex relationship with Fenris because he was my favorite character in that game besides Hawke and Varric(sp?)