the start is a person who feels anxiety from their realization that alone they are vulnerable to the hostile forces of nature and society. "Alone" is essentially as in this thread. Then how to respond? From Fromm, love of god is one possible response -- some people suppress a lot anxiety that way and, maybe, have some forms of bonding that can help them in practical ways. Another response is love of spouse -- that's what's central in this thread. A third response is to join a group, that might tribal in some sense, political, religious, etc. -- but being in the group can help do something, hopefully productive, about the aloneness, vulnerability, and anxiety.
A biggie point is Fromm's explanation of love of spouse as a response to the anxiety and not much like the pop culture version of love. To be blunt, porn is Fromm's (iv) and misses all of the benefits of his (i) to (iii). What they do in the porn shots is useless -- the actors don't even pay attention to each other, no kissing, bonding. It does nothing good and, of course, can do harm.
Fromm's book is short. Get some views of some of the clinical psychology or marriage counseling communities. Then, since the book is so short, just read the thing.
I'm just passing along what I learned paying full tuition, trying desperately to save the life of my wife, which I failed to do. Don't take my advice -- ask others as I suggested. Then, did I mention, the book is short? Again, did I mention that won't find Fromm's ideas in pop culture.
Experience with just one marriage would not be nearly such good information or yield such good ideas.