Ugh I get feeling jelous, but either tell her or stay that way - like, getting like this a...

Well if you see it in his pov, he has been holding back from the moment he met her again. When people being close to her, when he being declared favorism (by the girls), when she prioritized some other people over him, etc.. it would be natural for him to feel pressured and unfair , even bitter when he’s been the one putting her above everyone when she’s putting everyone above her - he might think his position is even behind some people.