I don’t even know where to start.
Why were you corresponding with a man like this at all? You are married. I know your marriage isn’t great, but you are married. If you find yourself corresponding with someone and you aren’t open about that with your husband (I am assuming your husband has no idea about this), then maybe you realize it’s not on the up and up to begin with. You aren’t innocent here. You hold some responsibility. Be smarter.
Good to hear you blocked him. Additionally, you probably need to delete your account on that forum. You’ve opened yourself up to scammers and predators. Bottom line: he did this because he’s a scammer and predator.
Stay off of random forums and social media if you can’t preventively lock your privacy settings so people can’t get to you. Don’t correspond privately with people on Internet forums. You don’t know who they are. That’s just basic internet adulting 101. This is how and why the scammers and predators of the world keep staying in business.