It's definitely never going to be 'and they all lived happily ever after', when you're looking at 40+ years (if you're lucky), through work woes, money worries, trying to conceive, having small kids, having big kids with student loans and relationship problems, having parents age and need help, and relations die, family tensions and marital break ups, inheritance issues, sickness, both physical and mental, young bods grow into creaky and flabby older bods, mortgages, failed businesses, addiction issues, cycling, golf, siblings and their families. . .
Everyone feeling really happy now?! 
A long term relationship has to weather a lot of shit. If you do it together, talking, with a similar sense of humour, and particularly if one of you can manage to stay strong when the other has to have a moment (but not always the same one staying strong, and the same one having a moment), you can definitely get there. . .