Why am I being forced to login from Steam

It sounds like you have two separate Path of Exile accounts.

If you would like to associate your Path of Exile account to Steam in order to use the Steam client, you can do this from the "Manage Connections" page which can be found here. You'll want to ensure you're logged into the account that you want to play using (you can double check this by looking for your characters at the top left of the page while you are logged in).

From there, you can link the account to Steam. If you've already used your Steam account to create or link to a different Path of Exile account, this may warn you about deleting the other account. You'll want to double check you're logged into the account you want to play before proceeding.

If you encounter any issues with this please feel free to contact us at support@grindinggear.com for further assistance!

Edit: If you're trying to log in using the stand-alone client you'll need to ensure you're signing into the correct account, using the same email and credentials you're using to log into the website. If you are logging into the website using your Steam credentials, you may first need to add an email address to your Path of Exile account via the "Manage Connections" page so you can use it to sign into the stand-alone client.

You would need to launch the stand-alone client. If you are launching the Steam client, it would use your Steam credentials.

You can download the stand-alone client here.