Back again - I don't understand exactly what do do.

Context: my partner is currently vetting a new potential partner. I can see the writing on the wall that it's going to happen and it just hasn't become official yet.

I am conflicted on the partner, but there's no hierarchical structure in terms where we both have to more or less be okay with it and she is happy it seems, so I don't have any issue with what's happening. That's to be expected.

The part that is bothering me is whenever we get in person time and hang out she is always and near constantly either checking her phone for a message from him or messaging him every few minutes. I may not be very well versed in the poly world, which is probably an understatement, but I don't think that stops being rude to be all over another partner and be mentally absent while physically present.

I am a demisexual so I'm very attracted to who she is and her mind, but it feels very much like - we'll if you're going to message him literally all the time I am here, why am I here? So I brought it up to her and she said since I get most of the in person time (considering I'm the only official partner, as of now, the math checks out I guess?) it's fair to check out of it more to text and message than it would be to do it to him - which is why it's not returned to me, and honestly I don't expect because I wouldn't want it done to me anyhow.

Am I stupid? I don't feel like I am missing anything.