Signing out of iCloud / Apple ID. Resetting old iPhone without it affecting my new iPhone?

I'm due to give my boyfriend my old iPhone as his is broken. I need to sign out of the iCloud settings and Apple ID on there but don't know my password for either of these. Some of my contacts have synced from my new phone to my old phone but nothing else has synced eg photos, apps etc. I'm scared that if I sign out of Apple ID on my old phone it will also sign out on my new phone. I turned off iMessage on my old phone, then it notified my new phone that this was tried. If I just factory reset my old phone, will it also reset my new phone as the two are linked?

Signing out or resetting won't affect another iPhone.

As a bonus, if you just log out, you can see what sites he's visiting on Safari. Just press the double square and scroll down.

That's not how it works, if you sign out then it only signs out of that device, it doesn't touch any other devices, the same with a reset.

I recommend going to https://www.icloud.com/...cloud.com/ on a computer and going through the "forgot your password" option so they you can set up a new password.