First of all, how horrid for you, I'm so sorry to read your post.
I agree the evening routine doesn't sound like too much fun for either of you, and you are now both 24yo?
I'll disagree with the 'other woman' idea, I don't think that's it.
I'm not patronising you in any way, I'm not doing that horrific 'you're so young thing' but I think you both have achieved/lived so much already, you may have hit a plateau.
It's tough to settle into a family life... jeez my DH is only now getting the hang of it, and he'll be 42 at the weekend....
You have both been so busy, renovating the house, having a family. Two boys a year apart? that's a lot of work, that's a lot of stuff to go through. For anyone, you guys are not even midway through your 20s!
When I was your age (OK we barely had accessible mobile phones, internet etc) but I wasn't anywhere near settling down, lookin after myself and taking on responsibility for myself, let alone 2 kids and a spouse.
How are YOU feeling in the marriage/family? You seem to sound fulfilled and settled, is it just him that has sprung this on you, or have you had your moments of wondering what on earth it was all about? We ALL do that BTW! I've practically worn that phrase out in my head it's been thought so much!
My opinion is that you both have been working so hard to get married, to get the house done, to have the kiddies that now you are struggling to find that happy family place.
he's keeping himself busy with solitary activity, perhaps you've been busy being a mum till now etc.
Now you have got the really hard bit out of the way, you are doing your Taekwondo, enjoying the time to yourself again, which is utterly and completely understandable.
BUT!!
You both need to reconnect with each other.
You do need to switch that bloody telly off while eating and talk about his day, your day and find things to re-engage with each other.
Reaon I dont think there is anyone else, is that he said it's killing him he can't find how to reconnect with you again.
Go OUT for a meal, with friends if you have to, anything to get yourselves enjoying yourselves in each others company.. go to the cinema? at least then you'll have something to talk about over dinner...the actual film.
First step, cook him a lovely dinner, sit him down, telly off, candles on and tell him you love him and your greatest wish is to see him smile again and laugh his head off with you.
I think he needs some looking after, neither of you are old enough to lead a life revolving around telly xBox etc.
I know it was a shitty text, but perhaps it's better he sent it to you, rather than doing what so many men do, and bugger off and find someone else. so that now you both can work together to reconnect, to enjoy life and have some bloody fun! Look at this as an early warning, a light coming on to tell you that this life needs a damned good service!
Can you get a sitter?
Once a week you both need to do something together - just you and him. Date night! Best if you go out, or you could have a special dinner in, phones off, xBox off, computer off.... No MN either!!!!!
I don't think all is lost by any stretch of the imagination. At the moment, he's talking by text, try to get that to be talking in person, both need to listen and be calm, and want to do better for the other one.
Most important? DON'T PANIC! I'm sure you can get past this, it'll take work, but you both have so much energy to put into projects, getting your marriage back on track is the next project for you both to undertake.