They are both experiencing what's known as NRE or "new relationship energy", the cocktail of hormones and emotions you get when you're first falling for someone. It often makes people act a little irrational, but if they understand what's going on it's usually easier to calm down. They're not trying to hurt you, they're just caught up in what they're feeling, but that doesn't mean you can't ask her to slow down a little and take your feelings into account too.
If you haven't already, do some reading about NRE, jealousy, poly time management, etc. Good resources at http://www.morethantwo.com/
and in the Golden Nuggets thread on these boards. Let her know that you're having a tough time, and when you find useful things in your reading, ask her to read them too. Tell her, and maybe him too, that it will probably be easier for you to open your heart and mind to being cool with them being together more if they can stay cool and be extra considerate and be patient with you now, at the beginning.
It's going to be ok!