they have to sit down to talk about it, but for me, i do think sex is important in a relationship. Especially when they are married, knowing the fact your friend doesn't enjoy sex as much as he does perhaps put him off abit

the guy needs to ask why is the girl feeling uncomfortable? perhaps he does something that makes her feel that way? If they really want to make this relationship works they need to solve this problem soon. I have a feeling that that guy might look for other sex partners if your friend refuse/dislike to have sex with him.

Sex can helps to improve a relationship, so if you ask whether it's important i'd definitely say yes, for both men and women