I could probably come up with a hundred different ways to show a guy you want to have sex with him. The problem is that they'd all involve showing off your dirty side in one way or another. If you're not comfortable enough with him to do that, then you won't like any of them. You're scared of being rejected, and anything you do to show your interest is going to carry that risk. I'd just focus on building up the trust in your relationship. When you have more of that, showing your interest will come more naturally. Until then, sex is going to be problematic.
“This planet has - or rather had - a problem, which was this: most of the people living on it were unhappy for pretty much of the time. Many solutions were suggested for this problem, but most of these were largely concerned with the movement of small green pieces of paper, which was odd because on the whole it wasn't the small green pieces of paper that were unhappy.” ― Douglas Adams, The Hitchhiker's Guide to the Galaxy