Yes. Just because you couldn't be in a relationship with them does not mean you can't stay friends. After the hurt has healed, and time has passed, a friendship with an ex can last a lifetime. One of my ex's was the photographer at my wedding, and he and I are like brother and sister. We ask advice of one another, and respect each other. He has been in a relationship for 17 years, and I have been married for 12. Neither of us thinks of the other in "that way".
I am also friends with my ex husband. We had two children together. I didn't want to be married to him, but that didn't mean I didn't want to be part of his life, with my children.
You can be friends...just friends...and share a lifetime of having a great friend by your side.