". . . You know how to interpret the appearance of the sky, but you cannot interpret the signs of the times. A wicked and adulterous generation looks for a miraculous sign, but none will be given it. . .". Matthew 16:3-4
Don't we all sometimes wish we had signs of what is to come? Well, there were multitudes surrounding Jesus and they were asking for signs. How many did they need? Feeding thousands with loaves and fishes, as well as healing the sick and raising the dead weren't enough?
If I understand correctly, he accused them of learning to interpret the signs of nature, but not the signs of future events.
Then he called them a wicked and adulterous generation who would get no miraculous signs. In this case, it seems he is, once again, using the term adultery to imply a lack of faithfulness to God, not a mate.
Don't you wonder how they could sit around the real miracle -- Jesus -- and ask for a miracle? He was quite justified in telling them they could not read the signs of miracles, or of the times.
How frustrated he must have been.