Not long ago a young woman asked the following question with regard to a new relationship.
"I am seeing a guy who is almost perfect for me in every way and I really like him but every time he talks about getting intimate I just want to run away. This isn't the first time I had that reaction, and I really don't want to lose him. So what is the best way to get over the fear or is it just one of those things where you just have to dive in and do?" – MN
Typically the fear of intimacy is the fear of being emotionally and/or physically close to another individual. Based upon what you state it does not sound like you have a fear of emotionally connecting with this guy. Oftentimes the fear of connecting physically is not so much about having a fear of the actual act of sex but more or less a fear of what may or may not happen after the relationship has gone to that level.
In some instances people worry about the quality or incompatibility as in suppose it's an "awful/disappointing experience" for one or both of you. They fear it could change how they relate to each other.
One of the reasons a lot of people recommend waiting to have sex until both people are "emotionally invested" or even married before having sex is because if things don't “click” right away there is a far more chance the couple will invest time and effort into learning how to improve things for each other.
On the other hand if there is no "emotional investment" on the part of both parties and one of you are "disappointed" there is chance that it may cause one of you to continue to search for a more "compatible" sexual partner. In other words if there is no real "emotional investment" people are not likely to "work on things” in a relationship. This causes some women in particular to feel "used".
The bottom line is one should never have sex with an agenda. By that I mean you don't want do it simply because the other person wants to or because you believe it will "solidify" your relationship and keep them from moving on. Know yourself, love yourself, and trust yourself.
You should only have sex because you want to! If there has been no talk about being "exclusive" or any indication the two of you plan to be together "long-term" then your having sex should have (no expectations) beyond hoping to be mutually satisfied.
Having sex with an "agenda" or the hope it will result in something else is what causes fear. It may also be a sign that on some level you don't trust his motives or the relationship at this point. Don't do anything before you are ready to. Remember you are responsible for your own choices in life.
If you "lose someone" it just means they're not "the one".