losing your dad and your beloved pet are very sad things that you have had to deal with.
What you are feeling is grief, sadness and loneliness. It sounds like complicated bereavement and people usually go through different stages of grief. Everyone is not the same.
Something to really see despite the current pain, is that you had a wonderful father and a sweet pet that lived to his old age. These are blessings. Not many people can say the same for their fathers.
A book that had helped me (and deal with loss is called Hello from Heaven) Another one is called Freddie the Leaf (it is more of a kid's book but it is presents us with a gentle reminder of impermanence which is the basis of all life)
Since you've mentioned that you feel more private, there are many online support groups you could join that deal with bereavement/grief issues.
Here is a link to one of my articles on dealing with the loss of a pet. Some of the things helped me say good bye to my furry kids.
The guilt you are feeling is not something they would want you to feel. You are grieving their loss/missing their presence. That is understandable. Your dad had given you life/he would want you to live it, enjoy it and cherish what you've learned from him. You also provided a good life for your pet being his mommy. If you remain feeling guilty, you'd be going against what they would want for you regardless where they are now/living on earth or existing in another place. Instead of focusing on the guilt, try to focus on the gifts that you have learned from them. Surely they are many = love, care, appreciation, responsibility, etc. and try to share these with others. In that way they will continue to live through you. Take one day at a time.