One powerful way to know for sure that you have a very strong chance of staying in a happy and healthy long term marriage is by making sure that you both develop your relationship maintenance skills.
In most cases the basic knowledge and skills for keeping the marriage healthy need to be learned and practiced at first, like the basic skills you need for driving a car. You don't want to drive without the proper training or it can really hurt all involved. Some people learn these skills from their parents and do the skills naturally that others must learn and practice until they become automatic.
Relationship maintenance skills are the same basic skills that emotionally distressed- couples use to save and affair-proof thier marriages as well.
These skills, which strong relationship-science and marital therapy research support, include learning how to identify, express and meet core relationship needs effectively and how to properly set protective boundaries around the relationship.