It sounds like you are in a relationship with a woman who we are calling Apple. And you have just started a romantic relationship with a man we are calling Banana. They are two individuals with different feelings and needs. There are two relationships.
How long have you been dating Apple?
Are you all new to poly?
It sounds like you've all already had talks, and determined that Apple is your "primary," making Banana your secondary. Is that true? How will this play out? Do you and Banana have some magical way of preventing your feelings from growing to the point where you feel they are your co-primaries?
Did Apple consent to Banana and you spending more time together and having sex? But now that you've done it, she's grown jealous?
Something GG didn't mention is that jealousy is based in fear. It sounds like Apple is fearful you will replace her in Banana's affections, or even force her out.
Is Banana not handling his NRE for you very well? (New relationship energy can be very overwhelming.)
Are you not handling YOUR NRE for Banana well?
Are you showing too many PDAs in front of Apple?
Are you three having threeway sex, and you and Banana are favoring each other?
What can YOU do in your actions to show Apple that you aren't trying to take her place?
Personally, I am not fond of triads, because there seems to always be jealousy between the established couple over their shared partner... This is almost inevitable. You might want to rethink dating/fucking Banana. I am NOT saying it's your intention to cowgirl Banana away from Apple, but sometimes established couples DO break up when they try and share a unicorn, and it goes badly.
It could be that Apple vetoes you and demands Banana and you break up.
It could be that Apple does that, and also breaks up with you.
It could be that Banana breaks up with Apple and stays with you.
It could be that you all break up and go your own ways.
Or maybe you'll work it out, the couple will feel reassured, and learn to share nicely.
Being jealous IS being upset, afraid of loss. Apple might also be envious. If you and Banana are often going off without her, she might not be managing that time alone well. She might feel rejected, unsure of her place, resentful of the newbie getting time with her partner of 10 years.
Did Apple start up with you to experiment with her bi side, but now Banana wants in on the act? Is this whole thing really okay?
You ARE coming between them, though, realistically. Their old relationship with each other is over. They have to forge a new one, where they are okay with each other having other loves/sexual partners. And in this case, they are both trying to date the same person! They might be better off dating individually.
Please read the book
Opening Up for much more information on how to successfully practice polyamory. There is also a good podcast called
Multiamory.
And here is a list of further resources: