Welcome to beyondblue forums. My best friend and I bought bicycles when we had our mid-life crises, turned out to be a better investment than sports cars.
His marriage broke up, but mine endured for which I'm grateful.
I suppose one text or phone call a week would be reasonable for letting him know how you feel yet still giving him space.
Though I suggest you ask him how much space he wants, like specific things about contact. Can you drop in to his new place to say hello? Can you buy him a birthday present when that's time? How often can you phone? Find some boundaries that show you care.
Also those boundaries are going to inform your decisions about your own needs. Are things open for negotiation anymore, like if he says call once a month and you want to call once a day, can compromise happen?
When I don't know what to do I gather information, research and think and feel about the situation.