She got mad that you didn’t wish her a happy birthday, given that at this stage in her relations with you, she has developed romantic feelings for you, and was hurt that you didn’t remember her birthday.

You believe that this shouldn’t be a big deal.

After all, you are not in a relationship with her.

Girls use a period of casual dating as a testing ground for how the guy could be as a boyfriend.

She isn’t casually dating you without any thought.

She is doing it for a reason.

Often, the reason is that she is testing you out.

She is observing what you say and do and trying to interpret what that says about you.

How would you act as a boyfriend?

How would you treat her as a girlfriend?

These are questions she has in her head the longer your casual relationship goes on.

In your mind, you believe that what you have with her is light and commitment-free.

The longer you are in this type of relationship with her, the more likely she judges your actions based on what she would want you to do as a boyfriend.

She becomes more attached and expectant.

This is what typically happens when casual relationships go beyond the one night stand and enter into weeks or months of hookups.

Feelings inevitably develop.

This is partly what makes human beings affectionate creatures.

Human beings are not robots.

A person can only go so far with someone else before they develop feelings.

This is what this girl is going through.

She is hurt that you didn’t wish her a happy birthday considering that she is already looking at you as a possible future boyfriend.

She has fantasized about how it would be.

She believes she knows you.

Now that you haven’t wished her a happy birthday she is upset that you have ruined that dream.

You ruined what she thought she had with you as far as feelings go.

Girls want to feel wanted and desired.

They want to know that they are special and be reminded of this on a regular basis.

This is often shown through affection, compliments and attention.

She likes to feel confident in the fact that you care.

This makes her feel special and wanted.

When you don’t wish her a happy birthday, she doesn’t feel special.

She doesn’t feel that you care, or that she is being paid the right kind of attention that she deserves.

You aren’t in a relationship with her, but she doesn’t see it that way.

She sees you as a very likely partner in the near future and you have just disappointed her.

This is most likely what she is thinking and how she is reacting to what you have just done.

She got a happy birthday wish from everyone else in her life who cares about her except you.

This is what disappoints her greatly and makes her feel hurt.

She wants the attention and you didn’t give it.