Hey joe,
Wow. There's a lot to unpack here.
I'm going to be so honest with you-- I think this is a shitty mentality to have. I felt really icky reading your post.
There's nothing *wrong* with casual sex, just for the record. If that's what you and this person both want, who am I to stop you? But I don't think you want casual sex. You just want sexual satisfaction (case in point: you said, "I want sex now.") If you're curious what the difference is, we have a great resource on casual sex and the work and respect between parties it actually requires:
Casual...Cool? Making Choices About Casual Sex
So you're attracted to this person just enough that you're willing to tolerate them because YOU want sex with another person? Which is what you want by the way. You're conflating "sex" with sexual activity with a partner. Highly recommend you check out this article here:
What Is Sex?
It sounds like to me you don't really like this person you just recognize that they are attractive and are willing to use them for your own pleasure. That's a really crappy way to view another human. That's a person with their own thoughts, feelings, and desires. I think the fact that you KNOW if you were honest with them about how you are feeling means that they wouldn't want to engage sexually with you says everything you need to know. You know this is a hurtful and reductive way to perceive another human being.
And yes, joe, forming a relationship with someone who you are actually interested in and is interested in you takes time, effort, communication, and respect. But that's what makes the relationship worth it. If you aren't in a place to pursue a long-term relationship, that's fine. But that doesn't mean you get to actively use and discard other people for your sexual pleasure.
For the record, someone being "attractive enough" is an extremely low marker for whether or not they are going to be a good, loving partner. Yes being attracted to someone is important, but I promise you that isn't what keeps relationships going long term. I know you're young and it probably feels really important right now. But you have to remember that you are going to get older. The people around you are going to get older. Your body and face will change. You could get into an accident and become disabled or disfigured. Being "attractive" is not a permanent state of being-- nor a universal truth.
My advice to you would be to do some soul-searching and think about what really matters to you in a relationship and why it feels like too much work to engage with other people in a way that might allow you to find someone you're actually interested in dating. I would also question why you perceive someone being attractive as an important metric for whether or not they are worth dating rather than any other quality they might bring to the table.
And in the meantime, I just have to ask: Why do you need to have sex with another person? Why can't you have sex with yourself if you need sex so badly?