I know I saw this episode. I have checked every episode of The Twilight Zone and Outer Limits. Can't find it. The episode is black and white. The astronaut returns to his home and there is a lot of interaction with his wife. He slowly realizes that there are changes occurring in his body as he is beginning to develop a crust or hard shell until eventually he morphs into a creature more like a large insect than anything human. Presumably he has contacted something in space which is triggering this metamorphosis into perhaps an alien species. There are scenes with NASA or space administration doctors who of course don’t know what’s happening to him either.
This may be The Quatermass Experiment, a 1953 black and white TV serial later made into a sci fi movie by Hammer Productions. A man retirns from space and morphs into a hard skinned plant, like creeping leprosy.
Along with his laboratory assistants, Professor Bernard Quatermass anxiously awaits the return to Earth of his new rocketship and its crew, who have become the first humans to travel into space. The rocket is at first thought to be lost, having dramatically overshot its planned orbit, but eventually it is detected by radar and returns to Earth, crash-landing in Wimbledon, London.
Carroon is abducted by a group of foreign agents whose government wants the information they believe obtained while travelling in space. It is clear that there is something critically wrong: he appears to have absorbed the consciousness of the other two crew members, and is slowly mutating into a plant-like alien organism.
It sounds a lot like the Doctor Who story The Ark In Space. That was colour, and broadcast in 1975.
The man doesn't have a wife, he has a female second in command.
The story is set on a space station. There's an alien who lays its eggs inside people. The infected people gradually change into aliens, who look like giant insects.
THe infection starts on a man's hand. https://ichef.bbci.co.uk/images/ic/624x351/p00vd75c.jpg
And finally turns him into an insect.
It doesn't match up perfectly to your description, but the first thing I thought of from your description was "Cold Hands, Warm Heart", an Outer Limits episode, starring William Shatner.
After completing the first manned mission to orbit Venus, astronaut Jeff Barton (Shatner) returns to Earth with recurring nightmares and an increasing inability to stay warm. Barton's condition continues to worsen and is accompanied by a peculiar webbing of his fingers. Only after his nightmares become more vivid does he recall an unrevealed alien encounter in the Venusian atmosphere. Barton's doctors suspect the astronaut had been genetically affected by his mission, and they then struggle to treat and cure him before his mutations completely take over.
It's been a long time since I've seen the episode, but my recollection is that Barton's transformation is reversed at the end, and he never stops looking mostly human.