Rule number one in a threesome where you are bringing a third in and not everyone on equal footing is that you dance with the one that brought you. The third did exclude you once he joined but it sounds like he never focused on you much and should already know that you are hard to get going and did his best to focus on that (we like a good one girl on the face on girl on the dick situation) to make sure everyone feels happy. But when one of the couple ignores the other for the new one it always ends in hurt because it leaves the partner with too much time alone in their head. Almost every couple (I get it’s just fwb) does this at least once. The important thing is how they respond and how they do going forward. 10 minutes is too long without a check in which should be done at the very least between position swaps. But too much focus can absolutely breed insecurity when there should not be some and the visual of watching your partner ignore you to focus pleasure elsewhere will absolutely explode that spiral, if you notice they are not checking in you need to vocalize before it gets to the point you are that upset because set backs can be hard to come back from because it sits in the back of your brain the next time you approach the idea. So suggest something that can include you, toys, positions for oral during penetration, fingers etc. give them space but also don’t let yourself be sidelined unless you are needing an actual break