How can I tell my stepmom I love her?

"You know, when you first moved into the house, I had a really big crush on you, silly isn't it?"

Be straight up with it. Be frank. Love is a strong emotion, but it does not have to be complicated. Sometimes being straight to the point, is the way to go.

just tell her you love her even if your dad dont

Tell her how you feel. That she is still special in your life....and maybe like another mother to you? Family isn't all about blood or decisions other people make as to marital status. Family is bigger than that.

If it's family love, then just find the right moment in a one-on-one conversation and say something like you were grateful for her and progress that into saying that you love and care for her. If it's romantic love, dunno what to tell you bud.