Why am I so shy around big crowds, but when I'm with one friend than I'm fine?

It sounds like you are experiencing Social Anxiety, you should look this up to be more aware of it, and try talking to someone about it, such as a therapist or family member/friend.

A crowd is full of strangers and can often times feel suffocating. You should be fine with your friends, that is a good sign because it shows that you are comfortable with them.

It is completely normal. I have the same problem. With a small crowd or even one person I feel very comfortable because it is one on one, but with a big crowd I get very scared.

That is very common. Crowds can be noisy and unpredictable. We can be afraid of being judged by people that we don't know.

You may be scared that someone is going to judge you. Though that shouldn't matter, Just be yourself

because in large crowds they are strangers and anxiety gets the best of you. Around a friend you took the time to get past the anxiety and open up.

This feeling you are experiencing is called social anxiety, this does not mean there is something wrong with you! I hope this gets better for you!

This happens because you are comfortable with your friend and know he/she most likely wouldn't do anything to harm you. So you put your guard down.

If you're around big crowds, you may feel that you have to surpass everyone present, in a way. You want to impress everyone, or at least not be put down by anyone, and this can be anxiety-inducing for some. For me, it means that I need to realize where I am and take a breather. If you're with one friend, you could be alright because the burden is not so heavy when it's just one pair of eyes on you, especially if you trust this person.

When you are with a friend you don't have any fear about judgement what it's not true when you are with strangers, making yourself more confident it's important to be more open to strange people,