Are iPhone texts being viewed on another device?

No.

They would need to be signed into your Apple Account and also need the Two Factor Authentication code sent to your device even if they know your Apple Account Password. That device would then appear in your Settings by tapping your name on top and scrolling to the bottom.

Now if you send a text to someone , that person can certainly forward your text to anyone they want, or take a screenshot of your communications and send it to them.

CuriousOne50 wrote:

I feel a close aquaintence has knowledge of my texts without actually reading them from my phone. Is it possible that my texts are being viewed on a device other than what i have them set to? Meaning not one of my devices that’s signed into my cloud account. I have an iPhone 17

If there other devices sharing the same Apple Account as you, then yes, absolutely anyone on your Apple Account has access to your text messages and your phone call logs and voicemail messages as well. You should NOT be sharing an Apple Account with anyone else, family or not.

Since you indicate you are, see this on how to separate accounts --> How to “unshare” an Apple ID - Apple Community

And this from Apple about why each person needs their own account --> Make sure that each family member has their own Apple Account - Apple Support

Is there any spyware or other means of monitoring someone’s phone......

No, there is not.

Since you are not sharing an account, no one has access to your messages unless you have provided them with your Apple Account name and Password.

If you are still not convinced.......run Safety Check on your iPhone.

Safety Check for an iPhone with iOS 16 or laterApple SupportOfficial Apple Support › guide › personal-safety › web

CuriousOne50 wrote:

I don’t think I indicated that I share an Apple account. If it reads that way I apologize for being unclear. No I do not share my account and I have changed my password recently incase it was being accessed.

It read that way as you said "not one of my devices that’s signed into my cloud account." I read that as there are other devices which are signed into your iCloud account. If you are NOT sharing an account with anyone, then no, they don't have access to your messages.

I don’t think I indicated that I share an Apple account. If it reads that way I apologize for being unclear. No I do not share my account and I have changed my password recently incase it was being accessed.

Thank you for your response. Is there any spyware or other means of monitoring someone’s phone that would allow knowledge of my texts or social media messages without the person having my passwords? I’ve researched and checked all the things suggested online yet I feel I could be missing something.

CuriousOne50 wrote:

Thank you for your response. Is there any spyware or other means of monitoring someone’s phone that would allow knowledge of my texts or social media messages without the person having my passwords? I’ve researched and checked all the things suggested online yet I feel I could be missing something.

No, there is not. The weakest link is the others that you do communicate with whether that is through a text or Social Media, and they can send that communication to anyone else.