what's the best ingredient to make relationship last?

Honesty and integrity. If you can't be honest with your partner you are going to have some serious problems in your relationship.

Communication first, then followed by trust and treating each other the way one would like to be treated.

I'd say trust, and honesty is important. But you need to be able to communicate openly and that goes with trust and honesty. You also have to be willing to put your own things aside for the other person, sometimes, but alos to be strong for yourself (not let the person walk all over you) It takes a lot of give and take.

patience, understanding, affection,

First of all, not getting into a relationship too fast. get to know each othervery well. after that, putting up with things you don't like about each other, not thinking you can find someone better. alot of times you can't.

trust is important, and being able to talk about everything with each other..

it really depends on the partners...we are all so different..and some like freedom,some are jalouse..some are open-minded some are more traditional..it just takes for us to choose the person that really suits for us,that likes the same things,that sees life the way we do...that complete us perfectly...there is no such recepy for a perfect relationship but if we find our soulmate it will be just fine

TRUST !! :)

i think that it is understanding an compation.

I would say trust, respect, and communication would make the relationship last. I'm doing it for 30 years with my hubby.

of course keep in contact with the loved ones be faithful don't expect too much don't take him/her for granted try not to hurt the emotions and ego

communication between each other. Being completely open to each other (i mean sharing the innest secret, not being physically open)

I feel trust is the one that will make a relationship last. besides trust forgiving and forgetting the mistakes committed by the other person also will make the relationship last long.