What do you think of me telling  someone I like her while I'm in a new long distance relationship
Are you serious? Why would you do that while in a relationship already?
I think she is the one
If you think she's the one you need to make sure you are honest with everyone first. They both will be mad at you if you start off by lying.
I just want some attention from somebody.
Long distance relationships can be lonely since you can't see the person but you cannot get attention from another person using dishonest means. When the person finds out that you are still in a relationship they will feel betrayed.