MNIONC, you are mourning not only the loss of your father, but also of your faith.
That's a lot to deal with.
When we reject our religion, we can end up adrift spiritually, no longer sure what we still believe. Figuring out what we do and don't believe after leaving a cult is a process that takes a lot of hard work. Many people, maybe even most, never do this work because it is so hard and often very painful emotionally.
Ironically, although we may have rejected some or even all of the specific, explicit beliefs of the religion, we often hold onto harmful core beliefs about ourselves and the world, beliefs which were expressed more implicitly. It's a bit of a Gordian Knot to untangle.
For example, we may have concluded that the seven men that call themselves the "Governing Body" are NOT God's earthly representatives, but we may still suffer from low self-image because of a lifetime of hearing that "God loves you, but if you screw up he's going to have to kill you at Armageddon." Translation: Nothing you do is ever good enough.
I hope that your writing about your feelings here and sharing them with us is helping you to sort it all out.
JP