Is it normal someone i hate so much is always on my mind?

My first proper girlfriend will almost certainly go down as my worst relationship but I think about her perhaps 4 or 5 times a week. Its been over half a year since the break up and I hate her for what she did to me. I won't go into all the details but the nail on the coffin was when we went on a group holiday after the break up (we had booked it months in advance). She was leading me on the entire holiday, making me think something could happen between us again including but not limited to her sleeping with me. She then got with one of my friends while I was in hospital, they are now going out. I never see her now as all my friends hate her as well, for what she did to me and them, except I can't forget her. I get angry when she pops into my head. Is there any way I can stop thinking of her?