Face ID

You can add your boyfriend's face here:

Settings > Face ID & Passcode > Set Up an Alternate Appearance.

Be aware that this will give him access to everything on your iPhone.

Hello ~ Take a look here by clicking on and reviewing the applicable information…

Set up Face ID on iPhone - Apple Support

~Katana-San~

Yes, you can add an alternate face.

I must have misunderstood it. But shouldn't the alternate face be another version of the same face?

EDIT:

After some quick research I found that Set Up an Alternate Appearance is fine for the purpose if you want to add one extra person. Sorry for the mistake.