Awkward
Meeting someone you met online can be very stressful and sometimes very awkward. Showing up and having them introduce you to their boyfriend would only make things even weirder. Finding out you are being interviewed to see if you are compatible with both has to make things extremely awkward.
What do you say to something like that? If that is your intention you should probably tell someone before you have them meet you somewhere with your boyfriend. I can’t even imagine what was going through his head when he met them.