"You are amazing. I am so grateful to have you" are good compliments which show that a person recognizes your worth.
"You're too good for me" is not a compliment. It's a red flag from someone who doesn't feel that they are good enough for you.
For you to make sense in their world, they will begin to look for things that are wrong with you and point them out. This can be quite upsetting, as you'll go from someone who could do no wrong to someone who can do no right. Even the tiniest, most unimportant things will be criticized.
Insecurity causes envy, spite, and being critical of others. You can't fix them, but you can avoid having your self-worth attacked by choosing not to pursue a relationship any further.