[TOMT] [Sci-fi novel] Multi are book with specific events.

I read it in the late 90s, but it could have been written in the 70s or 80s. Single character POV. Starts on an ice planet, male protagonist is a teenager. I remember they skated. He eventually goes undercover with other people to infiltrate a group Yeti-like people that live on the same planet. He is disgusted by eating raw meat and his group gets caught because he has sex with the girl who pretends to be his sister. The climax is that he goes to war with other people from his planet in FTL ships and they fight by jumping to the same spot in space and destroying each other. Their ships integrate with the pilot's brain.

I remember a lot of the book, but not the title/author and can't find it. Thanks in advanced.