you cannot expect someone to sustain a relationship with you, and satisfy your desires/need if you’re not the only person they’re dating

You're welcome to feel however you wish about relationships, but please don't assume how it works for you is how it works for everyone else. Being able to satisfy desires and needs has nothing to do with how many people you are dating, it has to do with matching needs/desires and willingness to fulfill them. Even in relationships which are monogamous, there are many folks who do not get all their needs and desires satisfied by their singular partner and are left wanting or find ways to get those needs filled elsewhere.

I also do not expect to get all of my needs met by one person. No one can do this. In many cases where people believe that they are doing this, they are often in codependent relationships. Humans are meant to be social, with many people, and to get their needs met by many. For example, you may have a friend or partner who is deeply supportive, but does not challenge you and a friend or partner who challenges you but may at times feel a bit less supportive because they challenge you - I would argue both of these are needs at different times for different situations, but it is extremely unlikely that you will find someone who is flexible enough to do both at the right times. In the same way, there are many needs that humans have that we get through our social support networks, and relying on a single person is, in my mind at least, either folly or cognitive dissonance.

try monogamy

I did a single 10 year long monogamous relationship, I was poly before it and poly after. There were many great things about that relationship and I still love her a lot, but monogamy just isn't right for me.