Honestly OP, I'm a similar age to you, and I know/work with quite a few men around the 24/26 age bracket.
When I read that he was that age, I just thought "ah. That'll be it then"
Men around that age tend to change a lot. It tends to be the age where the wild party boys settle down, and take up mountain climbing or something equally wholesome, and it's also when the university met-during-fresher's couples split up.
Given that you're a few years older, and given that you sound like the sort of person who is quite focused, thoughtful, and self aware, you're naturally going to assume that your DH is on the same wavelength.
However, if I'm honest, it sounds as though he's enjoyed the excitement, and then the comforts, of falling in love and getting married.
But now, I'm guessing things have changed, he's probably developed a bit more confidence now he's older, possibly finds he's more attractive to a wider range of women now he's "established"and not just a daft early 20s bloke, and he's essentially decided that he wants a girlfriend rather than a wife.
Relationships that he had before the age of 18 are quite frankly up there with holding hands in the playground, and I think you're holding on to that as a bit of a comfort blanket really, but dating Ashley from lower sixth for a few months does not make him an old hand at relationships.
He's still a lying, probably cheating twat and none of this is your fault, but I do feel that this is the start of something for him