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I'd say no. Look elsewhere to crush on someone. Your crushing on this person will cause you to stretch the limits of how you should behave, and you won't respect boundaries.

I'm trying really hard to stop

There is no such thing as okay or not okay when it comes to having a crush. You can't help who you crush on. There is okay and not okay on who you make a move on though.

So I have a few questions.

How old are you? How old is this crush? Does this crush have a boyfriend or girlfriend?

One thing that I will warn you about. If you're young, and this is a good friend, I'd look elsewhere. The majority of young relationships end, and once you've been boyfriend and girlfriend, being friends is really no longer an option, especially when you're young. So you have to decide whether you want to lose this friendship in the long run.

I'm trying really hard to stop
Is this the 20-25 year old woman in your other question? You have a crush on her?

https://www.askmehelpdesk.com/dating/okay-18-year-old-guy-date-20-25-year-old-girl-802512.html

No a girl at school

No a girl at school
As long as she's dating someone, it's hands (and heart) off. And if she become free, be careful you don't become a rebound boyfriend (they get dumped pretty fast), or worse, get put in the friend zone where she cries on your shoulder until she finds a rebound guy.

I'm 18 she's 17 yes she has a BF

I don't know if I like her or not I'm so confused I've only known her for about 6 weeks

As noted, she is dating someone else, so even if you had a crush, you do nothing,

So, can you have one, yes, no one can stop you. The issue is, you can not say or do anything about it, so it is best to try not to think about her that way

Ok case closed

Crushes come and go, and its okay to have a crush on anyone. It's what you do about that crush that counts. Just stay within the boundaries of good behavior.

Most high school relationships don't last, so one option is to wait it out. As another take on the situation, dating is not engaged and is not married. I don't like this idea that high school kids own each other because they date. I feel it is OK to let the young lady know you are interested in her. If she turns you down though, take her at her word. At the same time, it is totally uncool to do that if her boyfriend is also your buddy. Guy code. Overall though, as my now very happily married friend used to say to her boyfriend of many years, "no rings, no strings". Of course, we didn't sleep with our boyfriends in those days so I would consider that too. If someone is in a sexual relationship, I certainly would not suggest stepping in. And if the relationship she is in is exclusive, don't see her unless she first ends it.