Most people can generally tell right away if they are interested in someone; but everyone is different and some people may take longer to make those decisions than others. Also, you may find that you are immediately attracted to someone, and then as you get to know them, you uncover certain details about them that you don't really like, and your attraction to them can fade. It can also be the opposite of that, and you may not be attracted to someone right away, but over time that attraction can grow based on the foundation of the connection you've built with them.
However, the second situation you are describing sounds like the person is irrationally jealous or controlling. Making comments about how much attention you receive from other people is childish and comes across as insecure. Making comments about clothing you choose to wear should be a huge red flag, and you should have the confidence to know that you can dress and act in whichever way pleases you the most. That behavior may be common, but it isn't normal, nor is it healthy.
"Caring is not an advantage."