This is not the time to 'accept a challenge' you will be chasing that prize forever, hang on in there long enough and he'll get so used to you he'll never leave.
Is that ALL you want for yourself? Not that he loves you from the top of your head to the tip of your toes, only that you have put in the time and he's used to you?????
Eventually he'll think he ought to have some kids.... you'll be there waiting like a labrador at his knee... you have kids, and he prattles on with his life, not emotionally invested in you OR the family.
Relationships are hard enough, even when you do both set out with the starry eyes all consuming love and passion. But to start out a serious long term relationship when one really isn't that into or head over heels for the other... Relationship and Mental Health Suicide....
DON'T SETTLE for this, be adored, be loved and be cherished, it wears off a little anyway, but if it's not there in the beginning....
Two scenarios: One, that he's damaged by the girl that left him after 12 years.... (why did she leave him?? was he the same with her???)
In which case he's emotionally unavailable and in need of counselling and will need to do a lot of work to find how to love again.
Two: the other scenario is that he just isn't that into you.
After a year, tbh, it's time for you to move on. Why should you be left with someone incapable of loving you.
Ooh, another possibility.. you tell him it's over, you leave and he gets the kick up the arse he needs to realise he does love you.
If he doesn't then you are out anyway aren't you.
Stop wasting your time, and stop him wasting your life. Find your BLISS!!!