When I was 12, my mom met my now step dad. About 6 months later my dad moved out of state. Since then, my mom and step dad have married and had two kids. I've seen my biological father four times. I hear from him once every few months and FI has only met him once (when were together for 6 months) 3.5 years ago. My step dad stepped up to the plate and at 22 took care of my sister and I like his own children. When visioning my wedding, I see my step dad walking me down the aisle and I have already asked him and he accepted. My biological father expects to be walking me down the aisle. I love him but how do I break this to him?