Mutual respect/friendship/communication/sharing a strong homelife together--one that is pleasant and environmentally pleasing (like a haven)
Allowing each other to develop their own interests and then supporting each other in such. (Doesn't mean you have to participate with them all the time, but allow them to seek their own interests too)
My husband was a great example of this. He allowed me to have my own religion (JW) for several years and trusted that it was what I wanted and didn't interfere with my spirituality. Eventually I figured it out and escaped the Org and we still have a loving relationship despite my years of religious insanity. During that period of time I did not push my religion on him, but allowed him to develop interests that were important to him--some things that I don't participate in myself, but support him in his participation of such.
Be an interesting individual. In otherwords remain as individuals who enjoy each others company (things don't get boring that way because there is always something new to share.)
I see so many relationships become toxic over the years because people lose respect for each other after many years of feeding tto much negativity into their relationship. So I guess being loving, kind, understanding, supportive and positive towards each other is of utmost importance.
Well, that's my observations anyway, hope it helps--all the best to you and yours,
cybs