I suggest you do a tag search "new to polyamory" or "new to poly", or if you think you're monogamous, you can also search "mono/poly"
Do an online search for "polyamory jealousy". There are lots of good articles out there.
Don't forget to breath. Your feelings are normal and understandable.
Me: 48 - Married, straight, male
Shiela: My wife.
Suzanne: My FWB
Adam: Shiela's LDR