I think my parents are in a loveless marriage
It's sad if your parents never loved each other. Can you tell if this is true?
When I looked into my mother's eyes, I was convinced that she never loved my father.
That may be your speculation but you are can't be sure because if they don't love each other then you would not have been born and they would have been divorced. The odds are they love and cherish each other and you are just overthinking and being paranoid about it.
Ok I won't tell either of them, I'll keep this to myself.
Good, it is not good for a child to interfere in their parent's relationship. They need to work on their marriage on their own and you cannot force them to love and cherish each other.