How can I help him get through this?

your pops is in a funk and being a guy myself when a guy really falls for a woman and then is dumped its really hard for us to get out of it try and spend as much time with your dad as possible anything that will keep his mind off her only time will heal but do what you can to be there for him even if you have to make him do stuff with you try your best honey and he'll pull out of it.