Non-stutterer with a stuttering friend wants perspective

Non-stutterer with a stuttering friend wants perspective Hi guys, I’m not a stutterer but I have a friend who is. I was just wondering, is it impolite to finish your sentences for you if you’re struggling or would you rather someone wait? My fiancé and I were wondering how it actually feels when people do that so we wouldn’t offend him or make him uncomfortable. Thanks! 😃