I didn't know how to verbalize my answer to your question, just because closure means so many things for different people. So I went and did some research so that I can link you to some things that could help.
Creating closure doesn't mean that you're stopping the love that you have for a person. For example when someone dies, and create closure, when we let them go, that doesn't mean we stop loving them any less. We've just made peace with it. It's the same with relationships. Sometimes in the beginning you may have to close your heart while you're going through the process of finding that peace. But it doesn't have to stay closed to that person or to anyone else forever.
Here's a link on grief it talks about ways to heal from it: Coping with Grief and Loss: Support for Grieving and Bereavement
There are other links on grief, but this was at the top of the list.
Here is a quote in a thing I read on Closure (I didn't like the article itself but I liked this): "Closure, although it sounds final, doesn't have to be. It's a simple act of letting the past be just that. The past. It doesn't mean that you can't ever open it again to take a peak or that you can't ever have it again. But it does mean that you have to let it go as it was, because the way it was, is surely gone. And given that for whatever reason it didn't work, it is probably good that it can't be that way again. After all, it didn't work. Perhaps it wasn't meant to be, or that it was, but in a different form than the way it was."
For me Closure is making peace with the past. It isn't dismissing the event or the person. It's accepting the things that happened, so that I can move forward in life. It's really hard to do, and takes a lot of time. But when I think of closure I think of 'making' peace. It's not sayings it's over goodbye. It's letting the dust settle.
At least that's what it is to me. I know right now in my life I am seeking to continue to find closure/peace in a lot of unclosed areas of my life, while trying to keep on going. And I think it's worth it. Making peace and being at peace with oneself.
Easier said than done I know >,<, but when you're ready, it will happen.