The operators don't know the extent to which Warframes can think and feel, because they're too immature in regards to the void powers they have. They ARE children in mind and body.
Volt favors the room because of the water. It's a personal feeling that only this particular Volt suit holds, enjoying the feeling of being wet. He's also a fan of Sharkwing missions, when he gets the chance to go. Ivara likes the room because it's his, and his energy signature is literally soaked into the water of the room. It 'smells' like him.
Frames aren't humans though, and their minds form from the bleeding of the operators' minds into their own from the transference. There's a correlation between frame personality and operator personality, but it isn't 1 for 1. They grow based on use, performance, 'death' frequency, and other factors.
Sexuality is part of animal instinct with a side of human emotion. Some frames have an itch that needs scratching. Some adopt human emotion, to a degree and choose others they enjoy. But love and relationships are too abstract to really comprehend as something viable.
Volt and Ivara aren't exclusive. Volt has had times with Nidus and one time with Mag. Ivara has has dealings with Loki and Mirage.
Sex is viewed as a means to bond and progress growth. The act of it grows the frame in different ways, and can affect performance of the frame when they're around their "partners" in a variety of ways, ways the operators would see as power synergy and affinity gain.
As for the codpieces... The frames with them installed were doing so with that function in mind. Rhino was designed as an alpha make in many respects, and his body set accordingly. Volt was modeled after rodents biologically, hence his flighty fighting schema and... Breeding capacity. The actual breeding designs fell through, as infested flesh is near impossible to program without being infested. Other frames vary greatly in shape and size. Would you like a list?