Is my bestfriend jealous?

Three years ago I met a girl who at first glance many would be scared of...she seems like a mean girl. Den after talkin in cl we found we really understood eachother since we had both lost out father like year prior to meeting. We got close. Then I took da decision not to wear gles but contacts. She changed dat too within couple months. Then I started doin my makeup a certaun way...eyelines extending past da eye in a curve...she started it too. Then since I had more gut friends (since kinder) she started pullin me away from dem nd den started flirting wit dem. Last year b4 meeting my bf I had been talkin to a guy but den I stoped becauae she startwd talkin to him. Then I talked to another nd she went nd flirted nd started dating him. Finally...I stoped doun my make up and surely week later she did too. I love my friend but idk why shea like dis. Why is she so competitivr nd trys to hurt my relationship?