Why is Helena jealous of Hermia

Helena is jealous because she believes that Demetrius, the man Helena's father wants her to marry, is interested in Hermia. After the group goes into the woods, Puck uses a potion that leaves both Demetrius and Lysander in love with Hermia...... Helena isn't a happy camper and takes her anger out on Hermia because in Helena's eyes, Hermia always gets what she wants.

Helena is jealous because she is in love with Demetrius but Demetrius loves Hermia, her friend.