The phrase "deep feelings" refers to strong emotions that are felt deeply within one's heart or soul. These feelings can be positive, such as love, happiness, and contentment, or negative, such as sadness, anger, or grief. When someone talks about having deep feelings for another person, it means they have a very intense and profound emotional connection with that individual. The term "deep" in this context implies that the emotions run very deeply and are not superficial or fleeting.