So, you're a singer. Singers sing. Right? Do you sing along with singers you love? Who doesn't? But, how far will that get you to sounding as good as your favorite or sounding even better than her/him?
Granted, you can make some progress by trying to duplicate style, pitch, learn lyrics, and so forth, but that only takes you so far. As you know, singers sing with music and they don't have someone else to carry the tune for them. This kind of practice of singing with a singer can act like a crutch and actually put you on a plateau of no progress. The first step on up that mountain is to do a solo flight. First try it with silence. I'm not sure of the source, but my high school band director said that "music is a painting made on a canvas of silence". That is a great place to start! Sing it a capella (with no music).
Speaking of "a capella", did you know that is Italian, as is most music terminology? "Capella" is Italian for chapel. Chapels usually are so small that they don't have room for pianos or organs in them. So we don't mean to sing small, we just mean to sing without any instruments and we call that a capella. It is a great way to discover what you really know and what you are faking or are "mistaking". I just had to make that rhyme!