Yes, I can see what you are saying... and it's definitely got me thinking... <brain churning away>
I think much of what you say here is what I hold in mind when I use the word "love" - which is why I was so hesitant to use that word, because everyone tends to think of it in different ways. When I think of love, I think of both a noun and a verb component intertwined together - creating one strong band. I focused much on the verb component, because that tends to be a weakness in our society these days. However, I have to admit, it brings additional clarity to the conversation to split it out the way you have... I may adopt that approach in the future.

yea, it's easy to fall in and out of love. if the emotion of love [being 'in' love] is the foundation of a relationship, it'll crumble as these types of relationships become highly turbulent. i won't deny the emotional component that love brings, as it's like the icing on the cake, and perhaps this is where the fulfillment part of the relationship comes [at least in terms of how one feels]. however, as much as people say 'i love you' in place of 'i am in love with you,' when people break up, it's not because they're not in love with each other as much as the reality that they failed to love each other. even emotions need to be sustained and built upon through constant acts of kindness and positive thought, almost like a personal will that goes deeper than your feelings. perhaps this is why [IMHO] love is an intertwining of all the body, mind, heart and soul.
in the end love becomes a decision influenced by all faculties of your personal being, where the final decision is a soulful one. as such, i believe marriage is an everyday decision. an every-second decision to love the other person with one's entire being, and if one relied on feelings, sexual urges, intellectual conquests, etc... that person will find him/herself in a world of trouble, or worse, cause a world of trouble for the involved parties [spouse, kids, etc].
this all sounds very mechanical, i know. im a pretty big mushball myself, but when it comes to serious decision making [like promising to love someone forever], i shift gears and run on an extra couple of cylinders. my heart will let me know my destination, but my thoughts will decide how to get there, and my fuel will be my personal will to achieve balance in both.
my mind is still fuzzy... bleh!
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I think in relationships, there has to be understanding and acceptance of who the other person is, both the best of who they are as well as the worst of their flaws. A romantic relationship would require trust, understanding, and communication. Definitely, it would be good to have common interests, but I've also seen very different people come together and make a relationsihp work... of course its a lot of work and requires a lot of understanding and compromises and meeting each other half way.
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if two people wanna make the relationship work, that's a common interest