Be direct as possible with. Also, let him know things in advance, so that he doesn't get overwhelmed. "I'd like to go out sometime next week to dinner with you." It shouldn't be too difficult. I think NT women in particular are so used to just assuming other people know what their intentions are, hence the plethora of jokes "I think you know." line comes in. Honestly as someone who is high functioning, NT women can be so annoying with that, No offense. I can actually pick up on non-verbal cues, but they just make me mad when the person isn't direct. I mean, if I were dating a girl and I knew she was upset and kept telling me everything was fine, I would tell her "Okay, well don't complain to me later when I tried to help." So, anyway be direct. Don't assume he knows how you feel, unless you flat out tell him. If you're upset, tell him you're upset and why, don't assume he knows. Just practice not assuming.