Mine has always gone out on a set night of the week (weeknight not weekend) for a certain hobby, he's been doing it for over 20 years. He will only miss it if:
we are away on holiday
someone is in hospital
we have a baby less than a week old
he has to work late/away from home
it is our wedding anniversary, or my birthday, or the DC birthdays (he goes if its his own birthday)
He occasionally goes out on a weekend night - perhaps for a friends birthday, end of hobby season celebration, stag do, works 'unofficial' Christmas party - probably 5 times a year?
He does:
an occasional fishing trip, taking about 4-6 hours perhaps twice a year
kayaking maybe once a month in the summer, 3hrs or so
a couple of cycle rides a month, min. 2hr each
We tried a thing where I had a regular weekday evening to myself, but it just didnt feel necessary. I had nothing specific to go out for and it felt like a chore - anything I want to do which requires time to myself, I wish to do in my own home really, I.e. Reading, sunbathing, polishing my car, sorting out my wardrobe, making some new jewellery bits, so no point me going out 
I much prefer the flexibility of being able to say oh I'm going to so and so's house on Friday night for drinks and catch up, I'll be out til 4am all evening don't wait up. This happens probably once every 2-3 months. He's not keen on this, but a timely mention of his weekly activity soon nips that one in the bud!