I also came out to my parents in a letter when I entered my first long term relationship. At that time there was a distance of 2000 km between us so I did not have to face any music as it were. At first my mother, a devout Christian, refused to accept it and me, and banned me from her house. But as time went on she came to understand and accept and now she fully accepts. We never really speak about it, but I have no qualms introducing what she calls my "special friend" to her. She even acts like a mother-in-law with them!.
My advice is to do it sooner rather than later.