I think it depends on the situation? I like someone I have zero chance with (different religions, pretty sure the feeling isn't mutual oh and a damn ocean in the way) but I still want to stay as close to this person as possible because their friendship means a lot to me and I would be gutted if we couldn't be friends. Sometimes things aren't meant to be but it doesn't mean you shouldn't be friends because you can't be together.
Well I know this older guy he is 37 and I know I have no chance with at all. He is engaged. And I would never even try anything cos I know my place and were I stand but I couldn't imagine not having him in my life. I look up to him at lot so as long as u can handle being around them and don't get overly jealous when they talk about there gf/BF and it doesn't kill you inside then I think it's good to keep the relationship but if it's too hard then just keep away