Are you kidding me? Dude send a goddamn message! If I didn't hear from a guy I went on a date for 4 days I would have assumed he wasn't into me and move on.  Text her and be like, "Hey! I had a great time with you, we should do it again!"  As soon as you can! Just something simple, like, "thinking of ya!" Like goddamn just be honest. I would be like. "Hey. I hope you're doing good! I wasn't sure if it was too soon to message ya, but you're running through my mind all the time." I don't think there was a time me and my fiance stopped messaging each other once since we left our first date. Except for sleep and work of course.