It really comes back to how much you have built the person up in your mind.
Oftentimes, you will build them to such a high level that you don’t believe that you can measure up.
That will make you more self-conscious and as a result, you will find it hard to be yourself around the person.
If you can catch yourself whenever you start creating fantastical stories in your mind about what this person must be like as a person and about what a relationship with them would be like, you will be able to keep a firm hold of reality.
This is what will allow you to be yourself around the person because you have kept yourself from building them up to impossible heights.