I don't think people in relationships that work over a long time can always say that they "knew" from the very start that it was going to work out in the long term. I can only really speak about our relationship, which still contains mysteries and surprises - started going out at 12 and still together at 61. The relationship right now is what we have built - we have both learned about each others needs and aspirations, listened and learned what was important and on the whole tried to understand what makes the other person happy, how to keep the relationship on an even keel. It's a very complex thing - a relationship that is strong enough to cope with an the things that change gradually in life over time like the stresses of work, parenthood, friendships, etc, well as all the unexpected events - for us, a child becoming very ill, parents dying, unemployment, financial decisions gone wrong, other bad decisions. So if they're is anything to be distilled from what we have built it's come from communication that is constant, open, deep and wide ranging, brutally honesty - what we do has built trust. I like that our relationship is far from perfect - it never had been - both of us would agree that the very idea of perfection in anything in life is a ridiculous and unhelpful one - of the was every perfection in our lives or relationship it would have been for a very brief moment - we are changing all the time - how well you cope and individuals and as a couple comes down to how adaptable you are, how quickly and easily you can let go of things and embrace new things. I can't spell out every tiny facet of what is a hugely complicated dynamic that exists between us - wet never used the word love - like perfection, it's such an unhelpful, meaningless term - how can one word describe something so complex and ever changing? It's hard sometimes to even generalise - there are contradictions in many areas of our lives. I would say we both see "the relationship" as something that of fig for both of us do we continue to invest in it rather than thinking about ourselves first above the relationship - there are conversations that have been like threads that have gone on for years - they are like a prevailing winds that keeps pushing the relationship in certain directions - for example, my wife wants to travel more than me so she pushes for that and I work towards meeting her needs, I try to make decisions with her that enable her to fulfill her dreams. I have many creative interests that she does not share but she works to try to accommodate what is for me a very deep need. We have quite different personalities in some ways - I am a dandelion that can flourish in any environment (all kinds of situations - social, work, business - I have a lot of self belief and confidence), my wife is an orchid who needs the exact right conditions to flourish - she doubts herself too much IMHO as she's is a very good judge of people and situations, far more intuitive than I am - so we see strengths in each other. Like most relationships in the first 15 years we went through some very emotional ups and downs - we were young, immature and had a lot to learn about ourselves, each other and how relationships work - we both came from similarly unstable/disrupted family backgrounds so we always think that what we sought and valued was stability - we didn't have it in our early home lives but we've tried to built it into our relationship - we can disagree and argue, debate and converse but we'd never say anything just to hurt the other person however heated a disagreement might be - we don't always manage to make up before bedtime but really, fall outs don't long - we don't get petty with each other, we quickly start doing the little things for each other that we normally do. As far as trust goes we both go all in - I think you have to - I could not trust anyone else as much as I trust my wife and in all areas of my life. So, in a nutshell, your relationship is what you build and the building never stops - we are committed to the relationship first because, overall, it makes life better for both of us.