I usually don't ask for help, but... - Comments

Another word for it is Marriage, buut that can clearly be taken as actual marriage. Hmm...
Here are all the synonyms for Relationship:

accord, affair, affiliation, affinity, alliance, analogy, appositeness, association, bond, communication, conjunction, consanguinity, consociation, contact, contingency, correlation, dependence, dependency, exchange, homogeneity, hookup, interconnection, interrelation, interrelationship, kinship, liaison, likeness, link, marriage, nearness, network, parallel, pertinence, pertinency, proportion, rapport, ratio, relation, relativity, relevance, similarity, tie, tie-in, tie-up.

Hope that helps xD