Missing my mom a lot

Today is my birthday in Chinese date, and I have been United States for 4 months. I still clearly remember the first day that I came to here with my parents and say 'goodbye' to them. I nearly cried, because it's the first time that my dad, mom and I all live different cities, and it's so difficult for my mom to meet my father and me. Friday night, my mom and I chated online, and she told me that I can buy something just as her present for me. Her words reminded me that it would be the first time that I celebrate my birthday and she isn't around me. It's so sick at heart for me. Maybe while we are growing, our parents are away from us step by step. Maybe I thought too much, and I just hope that my mom can take care of herself well.