I can so relate to your situation. Our divorce is not final but the waiting period is over and we are negotiating a property settlement. We would be married 20 year on October 4. I miss him every day. We have been separated for 12 1/2 months. H is dating a friend of ours that he dated a couple of times in high school. My therapist said we have a distancer/pursuer R and that if I stop pursuing he will stop distancing because he will not like how far he is from me. It s the hardest thing I have ever done. I feel the same as you that someday we will be together again. However, then I wonder if I am fooling myself. My H did the mixed messages thing from the time he told me he did not want to be married anymore 2 1/2 years ago. We have two boys 19 and 17. He has distanced from them, too. He spends no more than 2 hours a week with S17 usually not even that long. S19 is in college and he is pretty angry with H but still calls him on a regular basis.
I still love my husband and cannot imagine not loving him or never being with him again. I have no answers for you only more questions and a deep understanding of how you feel.
Keep your chin up.
Everything happens for a reason, maybe Dad needs to find that it isn't better out there, he needs to realize how good he had it here. Maybe he will find God and that is the most important thing when he finds Him he will know he is supposed to come home.