27 years

I just found out that my female best friend of 27 years has decided to become a trans-male and has begun the transition process. How would you recommend for me to process a large number of thoughts about this circumstance? Currently, my own feelings from my thoughts range from happiness to pain/loss of their female persona who I had so many amazing memories to a whole bunch of other feelings. My action is being outwardly supportive and to process this privately. Thanks for your help!