Lack of sex

My girlfriend is the love of my life and I will always love her. But lately the sex just stopped (like completely stopped) and I am unsure why. It gets to a point I have to beg her for anything. She doesn't want to have sex, give me a BJ or handjob. She doesn't even want to send quick pics of herself for me. I have talked to her about it and she says she is studying and busy. That I understand but then she still has time to go to kareoke with her friends and go to different events but doesn't have time to spend with me or even do anything sexual....... Also on the rare occasion she will make a sex joke and be dirty for like 5 min and I will get excited then she cuts it off and acts like nothing happened and I'm sitting here aroused. Any help