Hi Turtle - and welcome !
Hope you enjoy browsing here.
To offer just a simple word or two in response ....
First I'd suggest just explain to them exactly what you explained to us ! That simple. In a non-confrontational manner. Just share feelings.
Other than that I'd suggest getting clear in your head about the difference between jealousy & envy. Something that's discussed in some depth both here and on other poly sites. We all tend to throw the terms around interchangeably but that's only ok when everyone involved understands what our concern really is. Because the necessary action can be quite different.
Maybe for example it's simply a case of logistics that gives them more time together because of schedules that coincide - but conflict with yours. Who knows. It will come out as you get talking and I bet solutions CAN be found. As long as the true desire (and concern) is there on everyone's part it could be as simple as that.
Good luck !