Advice needed! Please dong just read. Give me a thought

So my big boy is 14 months and he already love his sister. 35w2d pregnant and I am ready to pop this girl out. But I think he must know she is almost here because his tantrum attacks are really bad lately. I tell him so many times a day that I love him and I know he don't understand but I also tell him that his daddy and I will love him and his sister the same that nothing will change. Any advice on what to do with his tantrum attacks? I love him dearly and I don't want his little self to feel like he is being replaced. Or is of me over thinking about it? I felt guilty when I got pregnant this time because I wanted to spend more time with him as a only child, but I feel that God allowed me to get pregnant because my dad was passing away and he was sending me a piece of my dad back ( since she will be born in my dad's birth month). Off topic sorry (pregnancy hormones) but I miss my dad so much. He has been gone for 4 months and I am sad he won't see my son grow or meet his granddaughter