My First Blowjob And Possibly The End Of My Relationship With My Girlfriend

The other night on a Friday, I was home alone when my parents were at a party. I invited my girlfriend (she is 15 years old and I'm 17 years old) over that night because we had been planning our first blowjob for a couple weeks. We were laying in bed and making out, mentally preparing ourselves for our first sexual encounter. She then slid underneath the bed covers and began giving me head. I was laying in bed half naked (without my pants, but I still had my shirt on) while she was underneath the blanket sucking me off. I'm not gonna lie...I consider myself lucky among guys for getting such a succulent, awesome blowjob, especially for the first time. I was so immersed in how good it felt, that I ejaculated in her mouth. Although it felt good, I was immediately terrified because I forgot to tell her I was about to c*m (we had agreed that I would not c*m in her mouth). She then threw off the blanket covers, threw her arms around my neck and kissed me. But unlike a romantic kiss, she transferred the c*m from her mouth into my own. She then stood up on the bed and stomped on my d*ck (It hurt a lot but luckily I survived) before she walked out of my house. As she left the house, I tried explaining to her that I didn't mean to c*m in her mouth like that. She hasn't spoken to me since. I don't know what to do. Please help me. I don't want our relationship to end. Please help. I would really appreciate it. I expect some mature responses.