WordNet sense 1 ((of a couple) existing together harmoniously):

well-matched

WordNet sense 2 (going well together; possessing harmonizing qualities):

matched

WordNet sense 3 (having similar disposition and tastes):

sympathetic

WordNet sense 4 (suitable to your needs or similar to your nature):

congenial

WordNet sense 5 ((chemistry, physics) capable of being mixed):

miscible, mixable

WordNet sense 6 (existing together in harmony):

harmonious

WordNet sense 7 (suitable or appropriate together):

congruous