Is it normal to want other people in a relationship?
Yes, it can be normal to feel attracted to other people or to want a relationship with more than one person. What matters is being honest and respecting the agreements everyone involved has made.
People can feel attraction to others even when they love their partner, and some people genuinely prefer consensual non-monogamy. Others are happiest in a monogamous relationship. Neither preference is automatically a problem—but wanting something different from your current arrangement is worth talking about honestly.
The key distinction is between a feeling or desire and what you do with it. Don’t assume your partner is okay with changing the rules; talk it through, listen to their answer, and don’t pressure them. If you want different things, that may be a real compatibility issue, not proof that either of you is wrong.