You can express to your crush that you have certain feelings for them just by your body language and the way, and amount of physical contact you maintain with them. It is very true that the way you behave around them and the way you treat them will affect the kind of relationship you end up developing with them in the future. Maintaining some amount of physical contact, like a touch on the arm or the occasional brushing of the legs can go a long way in telling your crush that you are there, and making yourself visible as a possible partner in their eyes.
