Why am I attracted to older guys when I'm already in a relationship?
Wrong question.
Being attracted to different guys is normal. It’s also unquestionable. When you’re attracted, you know you are. There’s no doubt about it. Why question it? It’s an immediate experience.
The real question is - why are you in a relationship? Being in a relationship is a status, a label, a thought. That’s not an immediate experience, it’s a description of your situation in life.
What does it mean to be in a relationship for you? Why did you make this arrangement? Are you seeking emotional support and comfort? Convenience? Easy access to sex? Being cared for or caring for someone? In what way?
Those are important questions.
There’s nothing wrong with being promiscuous. You can exit this relationship, go have sex with as many guys as you like, satisfy your yearning for variety and learn to not rely on anyone else other than yourself for emotional support. It might not be easy, but it might be worth it.
Or you can stay in the relationship, satisfy your yearning for one, and learn to suppress your attraction for other people, or channel it into sexual variety with your partner, or even experiment a little with other people together. It might not be easy, but it might be worth it.
You are the only one who can decide. There’s no right answer here. Nothing wrong with any choice you make. It’s your experience of life. Whatever you do, don’t let fear dictate what it will be like.