I’m worried about my crush being stolen

Stop viewing it as someone being 'stolen'. You're not in a relationship and presumably have never made any clear romantic advances.

If you want to date them, ask them out.

Be a man. Stop asking other people to do your work for you. You got yourself in this situation by being feeble. Find a way to ask her first.

I have actually been in a few relationships

I have actually been in a few relationships

How can I if this boy will be at the meet-up in September and I won’t be

Get her insta if your that paranoia of her being stolen away, even though your not in a relationship with her.

Hey guys,
I attend a nature reserve group at the weekends around once every one or two months and there’s a girl there that I fancy and she talks to a boy who I’ve started talking to although this boy tells me that they aren’t going out with each other.
I asked him to maybe help me with getting her as my girlfriend on the last meet-up at the September meet-up and he said that he could help put in a good word for me but I’ve just found out that I won’t be attending the September meet-up because my Mum has booked some tutoring sessions for me then so the next meet-up I will be attend will be the October one.
I’m worried that this boy might ask her out at the September meet-up as I won’t be there. Please give me some advice on this one guys.

My advice is don't wait until September / October to make a move on this girl if you like her. Do you have any of her contact details? If not, can you search for her on Social Media?

This other boy may or may not be interested in her... but she's likely to meet / encounter a whole load of other guys between now and September (it's summer, so people will be out and about a lot more than usual). What's to say someone else doesn't ask her out before either of you two?!?

And as others have said, until you officially become boyfriend and girlfriend, she's not "yours" to be "stolen from you".

Bottom line, if you want her to be your girlfriend, you need to let her know as soon as possible. Don't wait around, cause bottom line is:- You snooze, you lose.

I don’t know any of her contact details and I’m not going to search for her on social media as that would just be cyber stalking.
And as I already explained I am not going to the next nature reserve activity in September I’m going to it on October. I thought at first that I would go there in September but found out that my Mum had already booked some tutoring sessions for me then. I told this boy that I am interested in her and he’s going to be there at the next meet-up in September whereas I won’t be so I’m worried that he’ll ask her out then.

Is he more attractive?

No I think I’m more handsome

Can't you just ask your mother to rebook the tutoring session. State that you have a commitment already made to this nature group thing, it is close to your heart or whatever you think may work.

Even if you do go to the September one I don't think you are guaranteed anything. So don't get your hopes up. Also socialising with the girl will count for a lot, if you don't socialise much or at all with her then she may not feel that comfortable about seeing you as her bf. Possibly the other guy may just be a talkative type who may not have any interest in her beyond that. You may be freaking out about him asking her out but I'm not sure he would say about putting in a good word for you if he was interested. Either that or he is a little deceitful but if he does ask her it's her choice anyway just the way it is really.