As P'Chen stated, he wanted to surprise Tulip. Plus, he never prevented her from explaining herself. She yelled at him and stormed off. And is it really surprising that P'Chen would be upset to see a girl who professes her love for him to be in a super-close embrace with another guy and at the same saying, "I love you" when that sort of closeness is typically reserved for your significant other? Compounded with the fact that P'Chen already knew that those two had been dating (and had seen them together before), it would not be far-fetched to think that, while he was diligently waiting for Tulip to turn 18, she had already resumed her relationship with P'Rome. Frankly, I can't blame him for feeling a bit miffed, even humiliated when he thought that she would be pleased that he remembered her birthday and came to celebrate it with her only to find out that she had been partying away with another guy, and showed no signs whatsoever of being pleased to see him.
I agree, Tulip may not care about age but as an adult P'Chen can't ignore it, and he clearly said "until your birthday" it's obvious that he didn't mean "let's not meet again" tbh I don't understand why she was upset even
Perhaps it's a combination of simply not being in contact with the object of her affection for an extended period of time and the manipulative, negative influence of her overly agressive ex-boyfriend who has his mind set on being her number one. Or maybe she has a hearing problem.
With each new chapter, my esteem for Tulip crumbles just a bit more. For someone who supposedly is madly in love with P'Chen, you certainly didn't look very happy to see him. Instead of being happy that he came when he promised he would, you bitch at him and act like a spoiled brat, ruining what could otherwise have been the highlight of your birthday. You're making me think P'Chen would be better off if you were actually dating P'Rome so P'Chen could give up on you.