The right to marriage is without any kind of doubt a fundamental right under Article 21 of the Constitution of India. It appears there is unnecessary confusion about fundamental rights especially among the legal community, let me make the points clear:
1) Natural rights and human rights are basically the same. Fundamental rights are those natural rights/human rights which are fundamental to the enjoying of life. Without fundamental rights the life will become miserable.
2) Neither human rights or fundamental rights are being "provided", "created", "made" or "granted" by any government document, Charter or Constitution. The Constitution is merely guaranteeing already existing fundamental rights from infringement by the State. They are already there and being enjoyed by the society. The society in the past may not be enjoying some fundamental rights or being aware of it. But when the society starts enjoying them they become fundamental rights. For example essential services like the right to electricity or internet where not in existence before electricity was discovered or internet was created. But today since they are enjoyed by the society and life will become miserable without electricity or internet, they are officially guaranteed as fundamental rights in many countries.
3) It is not necessary that all the fundamental rights guaranteed under Part III of the Constitution need to be explicitly enumerated. For example the right to information, the right to keep and bear arms, the right to property are not explicitly enumerated under the Part III of the Constitution but they are without any doubt fundamental rights guaranteed under the Part III of the Constitution. To understand in detail one may read the following links: