I first want to say that living with another person is not always easy. Easy is something that we may want, so that we do not have to do the work that a strong relationship requires. The second thing is that none of us is perfect, and expecting the "other partner" to change to meet my needs, usually leads to disappointment.
I say this as a retired social work counselor who has worked with lots of people and been married to the same person for 50 years. To me, the foundation to a successful marriage is love. Without it on both sides the odds are slim it will last. But love is not something many people understand. If it was understood my most people, we would have a very different world. When I say love, I am not just talking about the emotion, but about its features like: non judgement, forgiveness, compassion, understanding, honesty, etc.
To truly love another you must first love yourself and see the beauty and strength within yourself. For if you can't see it in yourself, you likely can't see it in your partner.
Even with love for the other in both partners, that is not enough. We still need knowledge of the partner's needs wants and beliefs, and an ability to problem solve and compromise and be responsible for our actions.
That is a tall order. So the best one can do is to try to be the best self they can be.
Sometimes, even after both partners give it their best try, perhaps through counseling, or self improvement, it doesn't work. Ending a relationship is perhaps the best outcome for both people.
That would constitute the best advice I could give to those who are contemplating a marriage or long term relationship.