Everyone gets paranoid at some point, it's natural so don't worry about it.
You've said that he isn't that kind of guy, if he is the kind of guy that you think he is then you shouldn't have any problems. Try to put your paranoia aside and look at it for what it is, look at your relationship and look at how good it is. He is doing so much for you, he wouldn't just let things go after you two have slept together, and you two can talk to each other. He sounds like a good guy, just speak to him.
Everyone is scared of being hurt or losing someone that they care about, it's natural. Remember that this guy is with you for a reason, and if things don't work out then it's not the end of the world. You'll pick yourself up, dust yourself off and move on. You're more likely to lose him because you are keeping things from him rather from you being a little bit paranoid.
You aren't sounding like a little girl, everyone has been there, done that and bought the t-shirt. It happens to everyone at some point during their life, probably more than once. If this guy is willing to end things because of this, then he isn't the guy you think he is and he doesn't deserve you.