Poly relationship has problems?

Idk how ppl can be poly w/o having any problems. I've been in a trio(friendship) and it did not go well. Couldn't even be together for a year. I have a big problem with jealousy. When I see them talking to each other without me it makes me jealous to the point I want to punish myself for feeling that way(I didn't dw). I just don't understand how ppl can be in a poly relationship and somehow make it work(?) While here I can't even stand seeing my friends talking to each other w/o my fat ass getting jealous