Married man that won't quit

[StandardNameHere]

I have a weekly sport activity that I have been doing for a year or two and it also involves a certain amount of volunteer work on weekends but not a vast amount, anyways to my point, we are all a friendly bunch with a good age range from 18- 50 but there is one man around my age who has taken an interest in me.
For quick background we are both married with children!
First I thought he was just a flirt in general so didn't think too much of it but he has actually admitted to me that he has a crush on me.
Here's my problem: I have been polite and laughed it off in a 'oh your wife will kill you' then tried the 'well we are both married and it's a silly crush' but he won't leave it, to the point that I know he would happily start an affair and is messaging me constantly.
If it was another member of our group I would probably read him the riot act, report to leader, all the obvious reactions but the bigger problem is, he is the leader so if I report it or whatever then it's going to be me that has to leave (and won't be able to join another group, he is high up!)
How do I deal with this? I don't know how to make this stop without a fallout

Stop replying to his messages

It is shit, but you need to make it much more plain than the words you have used so far that it is completely unwanted. More along the lines of ' I have no interest whatsoever in your advances and if you continue at all I will be forced to report them to higher authorities. Please take this warning and back off!"

He’s an arse, not taking a telling. Make it clear and don’t say it in a nice way. If he continues speak in the group about the sexual harassment news stories in the papers and make sure he’s listening.

You probably are not the first woman that this man has put the moves on because he is the leader of the group and fancies himself
Leader or not you should have put a stop to this mans overtures imediately, not just laugh it off . Leader or not you need to tell this man to stop. Have you told your husband about the situation, I assume you have not. If you cant tell this man to back off maybe your husband should.
As for this man being "high up" in the organisation, you should report him. You claim you have his messages.
This is harrassment. You need to stand up for yourself.

I've had this at work before. In the end I blocked him on everything. At first I was very flattered and flirted back but then it went way too far. Block him!

Stop being polite. Message back clearly stating you want him to stop. If he doesn't you need to take it further. Don't feel bad about doing it, it's him who is in the wrong.

Tell him in no uncertain terms you aren't interested. And that you have told your husband. Have you? I would if he's the sort of partner that has your back.

You haven't yet told him to stop. Try tellig him outright to stop saying flirty things to you. Be firm and don't try to soften it. Women sometimes try to soften the blow because it makes it feel less unpleasant/awkward but remember that he is causing this unpleasant/awkward situation, not you.

Forward the messages to his wife. That should stop the gropy little shit in his tracks, and give her a much-needed heads-up as to what her "D"H is up to.

Is there any reason why you can't just block his number?

Tell him to fuck off or you’ll report him and tell the entire group why.

Stop replying to his messages.

Text this. Mate, I'm really not interested in you at all in that capacity. You're making me feel uncomfortable, so I'm telling you to stop.

Nothing else. If he carries on, then think of your next move. Stop replying to his messages too.

Does your husband know?

I’d text back

If you don’t stop texting me inappropriate messages I will have no choice but to report this.

Then actually think about changing your sim

I would initially start by telling him that you don't have affairs and are happily married. Only respond to messages which are professional in a very to the point way.

If this fails or he turns nasty then you will need to take it further. You may also be wise to say to whoever would deal with this there his manager / HR that you don't want anything done at present but he has been suggesting an affair with you.

I had a manager do this to me whilst his wife was pregnant. I tried ignoring him, just sent him into very angry moods. I told him I didn't have affairs, he just tried to persuade me. I told him if he carried on I had found his wife's phone number online and I would accept his offer of coming round to my house but would hide his wife in a cupboard so she could find out the type of man she was married to. He said I should. Argh!

I did say to his boss but said I didn't want anything done when he tried to give me a bad appraisal just after I rejected him. Appraisal got changed to fine. He left to go to another company and was trying to get me to go with him. Still married, had third child, wife posting how wonderful he is online. Good luck.

A lot of sports have governing bodies, and perhaps it's worth looking them up, and seeing what advice and support they offer in this situation.
As others have said, you may not be the firs, or only one this is happening to.

He’s probably a serial offender so just tell him to stop immediately as you’re married and not interested even if you were single.

If it’s his first Time doing this then tell him the same so he learns fast it’s bang out Of line

Whichever situation he needs to pack it in but clearly you’ve got to give him that message!

What @PricklyBall said