There is nothing wrong, with not wanting to be out socialising all of the time, when you are nearing 50. I am 46 and DH is 43, and aside from a meal out here and there, we are happiest having a nice meal and wine at home. I started pubbing and clubbing at 15 and slowed down around 38 - that's 23 years on the Razz and quite frankly I've had enough. Sounds like your DH has hit this wall as well.
Why are you still resentful of his diving weekends away? They were over 10 years ago? Seems a long time to hold a grudge.
Making contact with an old flame (if that's what he was), was a big mistake. He's making you think of a time that no longer exists. You can't have that life now, you have kids and grown up responsibilities. You can be wistful, but let's not get carried away!
So your DH gets in from working all day, makes dinner, and then sits down for a relax before bed. This seems pretty standard. What else is it you want him to be doing? If it's decorating, that would clearly have to wait until the weekend. If so, tell him that's the plan, order all the stuff on-line and be ready to go at it together on Saturday morning. Kids can also help.
I think you will see life as a bit more exciting as your children grow more independent, as that will mean more spare time for you. If they go to Uni, you've only got 3 years until the oldest goes and 7 years until you are child free. You could travel and take up new hobbies at this point. This is what me and DH are doing, as DC1 has flown the nest, with DC2 leaving in September.