iPhone vs non iPhone

If you have an iPhone, you can use Continuity to receive SMS messages on your iPad.

Follow the steps here to set it up:

Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support

You can, also, consider Yahoo Messenger.

When my now wife and I were dating, we both had incompatible devices and computers.

We both decided on Yahoo Messenger as it has both text messaging and video/audio conferencing capabilities.

Worked quite well for the both of us for over a year!

You and your friend can also use a common internet messaging app and service, like Skype or Google Hangouts if you don’t have an iPhone to pair with the iPad.