Looking for SF book title
I read this as a kid. Likely pre-1984. I'm probably murky on the details here. The lead characters were a man and a tall slender woman. An alien race that is taking over the universe captures the man and he is confined by himself for a long time. (I am facinated by solitude). They put the woman in with him as an experiment. (think planet of the apes). They end up a couple…go figure. The aliens surgically alter the woman to look like them. They have serrated lips that serve as teeth, Red tone skin, and a vertical row of alternating concave and convex hemispherical structures up the front of their torso that serve as sex organs. Drama ensues about her accepting her physical changes. He escapes, frees her and they escape to another planet. There he builds an alliance to resist the invaders. Lots of detail about weapons and ships. He ends up on the Alien’s planet. My memory gets even dimmer from there. I may not have finished it. I’d really like to find it and re-read. I was really struck by some of themes at the time.