How did you guys deal with your dad's new wife and his new baby after your mom's death?

Seeing my dad moving on with his new wife and a baby on the way feels so weird. I'm happy for him but what about me? I feel like a brick. Wish mom was still alive. Atleast I would've a back to lean on. I want to leave everyone and everything right now but my empathy and sensitive nature makes it so hard. Putting others needs and feelings first seems so hard to stop. I seriously need to get away from him and his new happy family. Because I'm now invisible to him.