If you can't or won't get married, which is itself a symbol of commitment, covenant, and promise, then how can you say, you have committed to your partner?
com·mit·ment
/kəˈmitmənt/Submit
noun
1.
the state or quality of being dedicated to a cause, activity, etc.
"the company's commitment to quality"
synonyms: dedication, devotion, allegiance, loyalty, faithfulness, fidelity, bond, adherence, attentiveness
"her commitment to her students continued undiminished"
2.
an engagement or obligation that restricts freedom of action.
"business commitments"
synonyms: responsibility, obligation, duty, tie, charge, liability, burden, pressure; More
I will agree that you can behave as if you are dedicated, you can come home everyday, not cheat, etc, but you are not committed in the sense of having a restriction upon your freedom.
To be married is to say 1) I will behave as if I am dedicated to you, AND 2) I agree to restrict my freedom of action, which means in this context that I will not cheat, nor leave you, until death do us part.
So I strongly disagree that marriage is unnecessary.
Also, it has always seemed ironic to me that people denounce marriage while still defending the idea of "committment", it seems the same as having a friend you cherish but never telling them so. Because the act of marriage is a public declaration of precisely the thing you say you want to offer "committment" and yet you are not offering.
Like a person who likes a friend, but never tells him/her so. Might they know you like them? Sure, will they ever know the full extent of your feelings? Probably not...
Whatever...