Is it really necessary to get married to have a healthy and loving relationship?
Does healthy and loving mean getting along or does it mean moral. If healthy means moral and God honoring than yes you should be married. If you view loving as simply getting along having good sex and so forth I believe you are missing out on an important and intense part of a relationship which is a real (NOT SUDO) spiritual connection that only comes when in a covenant relationship with God and your spouse.
A good relationship is based on the compatibility and love of two people not on the papers that they sign or the ceremonies in which they participate. Many people choose to live happily and healthily unmarried for years before they "make it official," if ever. Marriage can have some legal and tax benefits. It can also serve to fulfill a religious requirement or ease social or family pressure. However, people can live happily together without it.
A healthy and loving relationship comes from the two people in the relationship. It has nothing to do with a marriage certificate. Most people now live with each other before getting married. In most states after six months they are considered legally married. A piece of paper is for those who need it to feel extra secure in the relationship.
While on the balance I would say that those who get married tend to have more healthy and loving relationships, it may just be a correlation/causation fallacy. Irregardlessly, it is technically possible that two people could have a healthy and loving relationship without getting married.