Those are small and positive steps, Dilly. Do you have a standing arrangement for the dates? Do you arrange them, or does he, or do you take turns? Does it feel like rekindling the romance, or just friendly, or something else? He sounds still very stressed and exhausted. It's good he is making these small efforts though.
Do you think your DS is affected by his father being away and not knowing himself what the state of play is? I know you said earlier your kids were relieved, in some ways, to have him out of the house because he can be so awful over the winter. And that you hadn't been able to speak openly to them about the situation. What do they think is happening? Do you think they're worried about things, or have assumed one of you has had an affair, or something like that? It can be strange what goes on inside a teenager's head.
I hope you sleep well. I checked out that podcast you mentioned - Relationship Alive - last night and downloaded a couple of episodes to listen to tonight. I am sleeping a little better.