Monogamy is a form of patriarchal and capitalist control It was made default by the church by perpetuating marriage, introduced as a form of control by the rich to ensure that property and wealth is legally inherited from one man to another through his surname.
Monogamy is new
For the vast length of human history, we were polygynous (even as far back as cavemen, there's evidence of men with multiple wives) or socially monogamous (raising a child then moving on); permanent monogamy is a recent ideology that has been wrongly defaulted as the only normal and acceptable type of relationship.
Monogamy is very rare in other species
Bonobos for example are all bisexual, to them, having sex is as casual as us having a handshake, it is a sign of trust. There are only 3 other known species that are more monogamous than us: https://www.bbc.co.uk/news/articles/c4gpvx3exglo
Less than 5% of species are monogamous. Pair-bonding may have played a part in our evolution, but single parenting is totally valid in modern day.
Attraction and attachment are separate systems
Our brains are hardwired to desire new experiences, meaning it's normal to find multiple people attractive. Lust, romantic attraction, sexual attraction, and attachment (security, love, close friendship) boil down to two separate and competing neurological systems - looking for something novel yet stable. Your brain desires two completely conflicting things: safety, and new experiences. They both have corresponding chemical pairs to go with them. That doesn't mean you have to get all from the same person, or even the same sex or gender. Equally no one should be judged for being open or closed. There's also no reason why you can't have a deep connection with multiple people at once. Sex can absolutely just be about pleasure; love or a deep connection is not a requirement.
Communication is key
Despite effort required in poly relationships, monogamy may also come from a deep insecurity and jealousy - a fear of being rejected, forgotten, missing out. But the key to any relationship is two-way communication, potentially leading to compersion (joy of seeing a partner happy), honesty, and allowing a relationship to evolve.
For me personally, I don't necessarily need a connection to have fun, but I at least need trust and boundaries. However my one condition to love someone is to have an unspoken bond.
YOLO
We only live once - is it really worth limiting yourself and not having fun, and bonding with others? As long as it's consensual, safe and hygienic.