I can totally relate. My mom passed away 5 years before I had my first baby. In my case, my dad remarried and that complicated matters further. Without going into my whole life story, I will just pass on some thoughts based on what I've learned. My oldest child is now 7, and my baby is a year old.
It is a GREAT idea to talk with your dad. It may give you both some comfort and help open communication which will strengthen your relationship. It is also important to know that you CANNOT CHANGE others. It hurts when it seems that loved ones cannot share in your joy. The truth is, it is their issue and they have to deal with it. In the meantime, if you have supportive and loving in-laws you should focus on that!! Feed on the positive energy and those that are thrilled that this baby is coming. I don't even know you and I am so happy for you. It is hard when our "family of origin" lets us down so to speak, but the good news is :You are building your own family. It is more important that you, your husband, and first child rejoice and celebrate this new blessing. This baby is a gift. Don't let ANYONE steal your joy- even if it is your dad.
I still struggle. I still miss my mom. I still get disappointed when grandparents do not seem as interested as I feel they should be. But, at the end of the day, I thank my lucky stars for my 2 beautiful children and my husband. We have a great family and that is all that counts. When my dad does come through, it is thrilling, because I'm not expecting it anymore.
Have a great pregnancy!