I married my "high school sweetheart" but he was across an ocean. We grew up and apart, as simple as that. We divorced after I'd tried just about everything I knew to try and repair our growing differences and resentment (and he dropped a bomb on me). Thing is, I'd changed and grown up and he had a kind of Peter Pan way of life that he enjoyed.
At the time we divorced, I felt like a huge failure. But after healing I realized that temporary relationships are just part of life, even those that seem unbreakable.
While you should know for sure and you clearly want to give it your all, you should not blame yourself or feel like a failure if you do not succeed. It takes effort from both of you. If you're the only one doing that, it won't work.
"If you deliberately plan on being less than you are capable of being, then I warn you that you'll be unhappy for the rest of your life."
~ Abraham Maslow