Could you elaborate on this point plz
Yes. Being in a committed relationship by choice means you are committing over and over again to stay and keep at it even after the initial blush of falling in love wears off (and it does wear off). It affects every part of your life and your decision making. It can take seven years to know a person, they say, and I can attest to it taking quite some time, in truth.
It can be extremely rewarding to work through life closely with another person. That encourages growth, as do relationships that do NOT work out. You learn about yourself, a great deal, by seeing how your actions and reactions affect another person who is so close to you.
If you did not maintain a close committed relationship you would never learn any of those things, you would never have opportunity.
When I said you should not become a reflection what I meant was that it is important to stay yourself, to be true to yourself, even while being true to another person. You cannot be what another person wishes you to be and nor are you what they see you as. So while you need to work with another person in the relationship you cannot forget, neglect, or change your own self to suit them. You need balance and a strong sense of self, which ironically, I feel is gained by being in a relationship as much as it is cemented by being alone.
My disclaimer here is that I have three failed marriages and I come from an unloving family. So use salt with my opinion.