When it comes to text messages, if I send something to both of my beloveds I make sure that the wording is such that they both know that. So, instead of saying "I love you" I will say "I love you both". That way nothing is hidden. I also send individual messages too.
As for the "should I get upset about this?" question - if you are upset, then yes, you should get upset! It's not a question of what should upset you - if something upsets you, then it upsets you, and it should be talked about, treated with respect and worked on as a team. You have a right to feel the way you do about other people's actions. Own that.
Please check out The Birdcage - an open, friendly Polyamory forum for all parts of New York State
"Listen, or your tongue will make you deaf." - Native American Proverb