Try the NVC style to express yourself: observing, and then asking. For example, "I haven't heard from you in several days. Have I done something that upset you?" Maybe the person is upset, maybe just busy, or maybe something else is going on. Try asking about it a little and see if you can get a straight answer. (Most autistic people are good at being honest, although they may be hesitant if they think you wouldn't like what they have to say.) You may get an answer, or you may not. If not, let it go. Assume that it's some problem related to the other person, and look for someone who is more interested in a date.