Eren:

Eren gets jealous easily. However, sometimes he won't even notice if a guy is flirting with you. When he is jealous, however, it normally ends up in anger, or trying to fight the guy. As much as you dislike Eren fighting others for you, you think it is a sweet motion.

Armin:

Armin is straightforward with jealousy. He'll normally tap on your shoulder and ask to talk to you in private. He will admit his feelings to you, and then apologize afterwards. You smile at the end, telling him there is nothing to apologize for.

Levi:

As much as he refuses to admit it, Levi is very envious. He will normally separate himself, and watch you from a distance. When Levi decides to intervene, he'll normally punish the cadet or slap the person who is making him jealous. Levi doesn't care who it is because he just wants you to himself.

Erwin:

Erwin is respectful when it comes to jealousy. He never admits that he's jealous. However you can clearly tell when he is. Erwin will wrap his arms around you, or hold your hand, or even stealing a small kiss. That shows enough.

Marco:

Marco is very kind when it comes to being envious. He will politely join your conversation with the person. Sometimes he'll give you glances that show his jealousy, and you'll understand completely.

Jean:

Jean takes jealousy too far. He will directly call the poor person out and fight them or insult them. You normally leave the room from embarrassment or watch and apologize to the person. Jean afterwards will kiss you to prove that you are his.