I'm in a relationship, but I don't know if I'm in love with him. What should I do?
Well, do you think that you are in love?
No, I just liked his appearance.
If you do not think that this could lead to love, you should not lead them on. It is going to hurt worse in the long run.
How do you know what relationship I am in?
Whatever relationship you are in, you shouldn't lead him on. If you break up with him now because you don't love him, he can get over it sooner and you can both move on to better things.