First of all, no bike is going to last forever and unless you are crashing, all frame materials will likely hold up to regular use. What usually makes bikes obsolete are changing standards and expectations. Personally, I don’t care one iota about frame material. While my heart loves their looks, my head is slightly biased against titanium bikes, simply because they tend to be more expensive and heavier than carbon frames.
Typically, independently of frame material frames will outlast all other components (again, unless you crash or have an accident), and IMHO a major factor is standards. My previous mountain bike (10 years old, aluminum) went obsolete, because it was the last generation of 26" mountain bikes, did not have through axles, etc. So I was unable to find a modern components for it and e. g. its fork and damper were on its last legs. On road bikes the churn of standards is slower, but it is still happening. E. g. rim brakes are going away, and in 10 years I reckon you will not get parts for rim brake bikes.
Another reason you might want a new bike is features. For example, you discover the magic of gravel riding and suddenly your road frame won’t work for you, because it cannot fit 40 mm tires.
I had a look at your post. While you write that you are riding “almost exclusively road”, you live in BC with lots of options for offroading (I hear). You also wrote you don’t want to race and it doesn’t seem like you want to squeeze every last ml of performance out of your bike. So I’d recommend you get something like the Open UP, 3T Exploro or similar bikes from Moot and the like. They will handle like (endurance) road bikes, but accept wide tires. The Open UP and the Exploro accept 2.1" mountain bike tires, but you can use 28 mm road tires on them as well if you prefer. And on road tires, they will handle exactly like a road bike and most people won’t notice the extra clearance. Depending on your wallet, these machines are not heavy. Rides of Japan’s Open UP was eventually no longer UCI legal, i. e. lighter than 6.8 kg.
If speed isn’t your primary concern, but comfort is, I’d go for 35 mm tires, either slicks or something with minimal tread (depending on road conditions and whether you are riding in the wet). The tire much more than frame material determines comfort.
Secondly, I’d look at Rival eTap AXS or 105 as my groupset with potential specific updates (e. g. a Red crank or Ultegra IceTech rotors). There is no functional difference between 105-level components and up, only weight. The money you save here you should invest into contact points (handlebars, seat post, saddle and pedals), a power meter (this is the TR forum after all) and wheels — in that order. Yes, saddles can be expensive, but a good saddle and handlebars that suit you are so, so important. You are not going to ride a bike you don’t feel comfortable on.
Thirdly, let’s not kid ourselves, looks matter. I had a look at the site you linked to and some of their example bikes look really, really pretty. I also noticed that they offered versions with large clearance, which is what I’d recommend.
PS Don’t tell your partner that this is going to be your last bike. Otherwise you’ll get into a @Nate_Pearson situation where you made a promise that you probably should not have made 
