It's already tough to deal with jealousy issues when you are in a committed relationship!
Now, when you are friends, even best friends with someone, there is no commitment!
How can you claim someone who does not belong to you?!!!
In that situation, jealousy is an absolute waste of your time and energy!
It is destructive and frustrating for all those involved.
Get rid of that pattern and learn to be happy for her.
It's all explained in detailed over here:
Now is the time to expand your circle of friends! Having other alternatives will make you much less dependent on her.
Ultimately, you want total freedom for both of you!
Get this material:
It will save you lots of trouble!
To your power!