I think the best foundation for any relationship is HONESTY.
You can't have "Trust" without honesty and integrity being shown. To blindly trust someone is a conman's dream!
To Love someone you can't trust is asking for heartache. Lust can be exciting but there are 23 other hours in the day.
The next important trait is both people have to (want the same things and agree on how to get them). Chemistry,Lust, and Sexual Drives should also be in sync.
People who agree most of the time are much more happier than those trying to change each other to their way of thinking.
Opposites may attract for the short run but "like attracts like" for the long run. See below my recipe for relationship happiness.