Are these expressions familiar to you? Let me point out that "head over heels" is an idiom meaning to be in love with someone very much. It is commonly used with the word "fall." For example, "I'm falling head over heels for her."
Also, you may have heard the phrase "You complete me." It became very popular after the movie Jerry McGuire with the actor Tom Cruise. Have you ever seen that movie? "You complete me" means you are incomplete without that person. That person makes your life perfect and gives you meaning to your life.
Of course, saying a simple "I love you" never gets old! How will you celebrate Valentine's Day this year?