**This is just my opinion.**
Firstly, Aryan wasn't jealous, he was irritated with Imlie always getting carried away in her emotions. Emotions hone ka matlab ye nahi that you just flow away with the tide, emotions make you human and feel. But Imlie is emotional to a fault. Giving away your emotions and feelings to a person who doesn't care for it is unhealthy and draining on the person who gives it away. Aryan had asked her to feel everything and not be stoic like him, but usko bhi niyantran aur santulan me rakhna padta hai. Infact, what Aryan said is what we all have been saying for ages. Imlie's "feelings" and "words" have no integrity. She retracts from it the very next episode. So, either don't give such heavy-duty dialogues to a child-woman or don't make her flip so often.
Second, Aryan wasn't possessive either. He isn't in that territory. Of course, he feels for her which overlaps with his mentorship, but he doesn't have that ownership over Imlie just yet. I am not saying it won't happen, but I am also saying that he isn't totally there yet.
Imlie and Aryan are in a zone, where there is an unspoken, unnamed bond between them which they don't want to justify or name. They get each other and they don't really shy away from being honest with each other. But there is a lot more untapped with this pair. Their sheer clarity and transparency in the communication make the intimacy game so strong, it just makes you feel you are interfering something rather private. It is subtle and slow but works for me. And whenever they do fall in love, it will be very intense, because its just simmering under that skin, with Imlie slowly beginning to acknowledge that Aryan's PoV matters, and Aryan acknowledging how much emotion and dedication this girl holds in her heart.