Keeping them together

As i told ya'll my friends come to me when it comes to relationships and their problems and lately they have been coming to me more than usual. Anyway my friend came to me and told me she wanted to leave her boyfriend of 3 years. When i asked her why she kind of studdard and ran around the bush with the answer. I was reading her actions and i realize she must want to leave for no reason. Now because this was her business i should have just told her to leave him or do whatever your heart desires but i couldn't give her just any information because that would give me a bad rep for my advice giving sessions. Anyway she finally told me why she wanted to leave and she was like she wants to leaves because the s*x isn't good anymore. Now i mean i know s*x is a major factor but i mean she has been with this guy for 3 years and 2 years and 5 months she has been sleeping with him(so she counted) and im just wondering do guys start off doing they job in the bed and then just stop? I doubted it. So i search and asked questions to get to the bottom and she's like i found someone thats better. I told that she should never leave because the s*x is bad and go to someone else because its better because that guy that you leaving for will leave you because some other girl is better. I asked her did she care for this guy but she said she really needed a better endept s*x life. My question is, Is s*x that big of a deal that it could make or break a relationship? Let me know cause that is something i need to know as a virgin. I dont want to end up like my friend and leave a guy cause the s*x is bad or because me and my loved one has a different mind frame on why how and when we need to have s*x. Let me know.
im out
Shonda