If someone else is logged onto icloud on my phone would they have access to my text messages?

Camelot wrote:

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AFAIK this doesn't apply to SMS messages, only iMessages (i.e. ones that appear in blue (iMessage) vs. green (SMS)), so it depends in part on the sender.

Yes, you can also get SMS on your Mac as well as iPad.

Messages (El Capitan): Get and send SMS messages

How would I know whether sms forwarding has been enabled?

1) You would have had to enable it, so your own memory is the first gauge.

2) On the device, check Settings -> Messages -> Text Message Forwarding

However, neither of these will affect messages already sent/delivered, only future deliveries.

Maybe you should be considering damage control.

Yes, it's entirely possible. iMessages sent to your phone may appear on your iPad and in Messages.app on your Mac if they're signed in to the same iCloud account.

AFAIK this doesn't apply to SMS messages, only iMessages (i.e. ones that appear in blue (iMessage) vs. green (SMS)), so it depends in part on the sender.

Yes, you can also get SMS on your Mac as well as iPad.

True, but only if you've enabled SMS forwarding, which few people do unintentionally, so I doubt is the situation here. This contrasts with iMessages, which automatically share across logged-in devices.

Yes, he can.

You'll need to sign out his Apple ID in Settings > Messages > Apple ID as well as in uncheck his phone & e-mail address(es) in Send & Receive

Droid send the standard SMS so if configured correctly, he can.

FWIW, I do get Samsung's SMS on my Mac & iPad from my contact.

It applies when using the same Apple ID.

He has to, let him sign out himself. There's no way around that.

You can check

Settings > Messages > Text Message Forwarding > here

What version of iOS have you?

Settings > General > About > find it here.