I would say Tolerance, because that's what I always hope I'll get. I think accepting something you don't like about someone is something you have to do if you want a relationship to last.

Communication and loyalty, certainly.

Mine fell apart due to a lack of communications and many misunderstandings... We had pretty much everything else.

At least any 3 out of 5 of those options are what make a relationship work. Having all of them are what Love songs are about.

loyalty..
you dont have to say everything.. and it may not always be fun.. or passionate.. relationships are all about ups and downs.. but as long as you stay loyal.. you can overcome those baddie moments.. i think..

if there's communication, the other options may happen

I picked tolerance because with enough of it all your problems will be solved.
don't kid yourself you're bound to have fun with any person you please if you put your mind to it.
passion is purely physical - in my opinion- so it's something everybody could work on.
and about loyalty no one likes to cheat on their loved ones it just happens, eventually everybody slips up but the key here is to forgive enter tolerance.
and in my opinion communication is something that gets better with time, you'll learn to pick up the subtle hints and whatnot.

All of the above.

Although I picked "Communication" because without it then you can have none of the other options.

Haru Totetsu: Communication.
I know with all these other methods of getting in touch with people it seems easy but its not. Most hide part of themselves from the rest of the world, the part of them they don't like, and not sharing that will lead to you and your loved ones keeping secrets from one another. Its hard showing the world all of who you are because that means facing your own faults and fears, but if you can't show all of who your are to someone then you don't trust them, and without any trust between you, how can you expect a relationship to progress.

Afetr that I'd say Loyalty and Tolerance go hand in hand. You have to be able to tolerate all of someone, to even want to be loyal to them, and vice versa really.

Fun and Passion also go hand in hand quite well I think, making your displays of passion for them something thats also fun for the both of you shows that you put real thought into all you do for them and would show to that special person just how deeply you think about them.

So really the mst crucial part to any relationship I guess is Balence. Finding that middle ground that suits both, your and their needs, like finding a good mix between work and play.

TRUST...

Where's truuustt