While there are many factors involved as to why many relationships fall apart over time, I do believe that when two people are on the same page with their personal boundaries and possess the same value system, there is a much higher chance that the relationship will last for the long haul. In any relationship, it is essential to have those deep conversations with one another to ensure that both people think and feel the same about both the small things and more important aspects of a relationship. For example, how does the other person feel about cheating? How often does the person like to be in communication throughout the day? What is their preferred method of communication? While not every single answer has to be the same as yours, at the very least, it is good to know the answers to these questions. Aside from knowing this information to better understand one another, this will also help in determining how compatible you are with someone. If you recognize that there are a good amount of differences when it comes to your values and boundaries, that might be a good time to reassess the relationship and decide if it is the right one for you or not.
I think that this is often overlooked due to a lack of communication and open dialogue but issues do arise over time from these differences. It is okay to ask questions and to find out how your partner feels regarding things that are important to you. It is also healthy and appropriate to express what your personal boundaries and values are. If the other person is not on board with them, take that as a cue to move on. Remember that the right person would not only respect your boundaries but they would also have no problem honoring them.