Nothing is more motivating than a sincere compliment of one's behavior or character. Being moody is normal and unpredictable. Don't get down on yourself or others when you have a bad day. No one is happy all the time. Healthy people tolerate their mood swings.
Nothing is more devastating than loneliness.
That person should be your confidant, but also one who can help you look at yourself. They usually get defensive and counter-blame when confronted innocently or directly. They are so sensitive that they get hurt over even minor things. They are no fun to be around because their hostility, withdrawal, or persecution complex turn people off. If you feel this way, search for the sources, of your internal conflicts and be mature enough to do something about them constructively.