Here is what you can do:
Have your partner create their own personal Feeld profile.
Go to Feeld Settings (human symbol in the bottom right) > Edit Profile.
Tap on 'Invite your partner' and share the link with your partner (❗only one of you should perform this step).
Feeld will open via the App Store or Google Play; your partner will need to accept the invite, and once they do, you'll be linked.
To include your partner in one of your conversations, open the Connection in question, tap on the 3 dots in the top right-hand corner, and choose Add Partner.