I'm dating my half sister and I'm worried about what happens when our relationship ends

EDIT: I'm not going to answer every single person, but thank you for the amount of supportive comments I've received. There are a lot of you who are telling me I should be able to "just let it go" but I think you know full well that it's all very well to say that, it's not that easy to do.<br><br>I've been with her as long as I have because I can't let it go. There's a pattern of hurt through our relationship that I can't let go of and that I'm aware of. I'm no longer in love with her, but I am still in love with the idea of being with her and it's not easy to break up with her and I certainly can't break up with her because I feel angry at her. She doesn't deserve that and it wouldn't be right. <br><br>I have been seeing a therapist for 4 months now and it's been helping somewhat. I realise most of my problems are not with her but with my dad for not giving us a childhood. I'm sorry, I don't think there's going to be any update that most of you are looking for, because it's probably not going to be good. We're just going to talk about things when we're both ready to.<br><br>We're not going to break up quick or nasty because I'm unable to do that, and it'd be horrible to do that to my sister. It's taken us 12 years to get to this point, I'm not ending it without giving us a chance to end it the best we can.<br><br>I'm not sure where this relationship as a whole is going to go, but I want to end it because I don't want to be with her and I don't want to be hurt by her again. I'm in pain from her, yes, but I'm also in pain because I feel like I'm failing as a brother and a partner and it's miserable to be in this position.<br><br>I've talked to her about breaking up and she knows that I don't really want to be together anymore and that we need to talk about it. I'm not going to talk to her about it until I can let go of sentiment and I can do it in a way that is respectful and caring, because I do love her a great deal, just not anymore in a romantic way.