According to me, mutual trust and respect are the founding stones necessary for the success of any relationship - atleast that's how I choose mine to be!! I cannot imagine myself being sincerely in love with anyone whom I can't respect. (Note: Respect and obedience are not the same in my dictionary. Mutual respect means that the comfort-level between two people is so high that they can agree to disagree. Obedience means that you're not allowed to have a conflicting point of view at all). I think it's impossible for me to keep a relationship alive if I cannot innately trust the other person. (Note: Trust does not mean blind faith. Trust allows for rational questions and arguments to arise so that you're reasonably convinced whereas blind faith doesn't allow for you to perceive facts).
I also think that for a relationship to be successful, you shouldn't take the other person for granted. One should understand that love, affection and trust are to be earned over time through actions which make one deserve them. Even after earning love by gaining trust & respect, it shouldn't be taken for granted. You should always act responsibly and be willing to take accountability for your actions later on as well, with the understanding that you might lose one's trust or affection if your actions are not worthy of them. This is what is meant by "not taking a relationship for granted". You can't act nasty and cause wanton damage to the other person and then come and say "please forgive me because I love you". Or you can't ignore that your partner is contributing much more than you for the relationship and make it up with "I love you so that should be enough". I don't mean contribution in terms of physical and/or financial contribution. These sort of words don't describe it - It goes beyond - I mean some sort of inner effort driven by an intense desire to keep the relationship happy.
As a natural corollary to avoid taking the other person for granted, avoiding ego conflicts is just as important to keep the relationship alive. In a relationship driven by mutual respect and responsibility, I don't think not having ego conflicts would rise any question of compromise on self-respect. In short, I think it's possible to avoid ego issues without compromising on self-respect - provided both the people in a relationship respect each other equally and act responsibly. Arguing about "why me? why me?" will be just as fruitful as the eternal debate about "Hen first or egg first?". Besides, genuine affection cannot be vulnerable to ego for long. When you love someone, you naturally want them to be happy and instinct cannot be suppressed by ego. One should never let ego stop oneself from saying sorry or expressing love to someone. Heck - one shouldn't let anything stop that - let alone ego!! It's never too much no matter how many times you say it. There's no need to wait for the right moment to do that - Time is now. Who knows when we'll be gone?
Like everything else in life, like education, career, character, including life itself, in a relationship too, there're phases and there is a need to progress/evolve with each phase. And each phase in a relationship also offers challenges similar to each phase in career, education etc. And it's necessary to accept this, acknowledge the challenges and work on them to progress to the next phase. Marriage is not some magical conclusion but just the beginning of another phase in a couple's relationship. It is neither necessary nor possible for two people to have the same taste, opinion and view on everything. As long as both of them allow each other enough personal space and freedom, relationship can have the potential to be long-lasting.