你很像我以前的女朋友。 ni hen xiang wo yiqian de nv peng you 不许减分。

No significant difference between "오빠 잘생겼다" and "오빠 잘생겼어". "-다" is the basic ending, "-어" is an ending for dark vowels, like ㅓ, ㅜ, ㅕ, ㅠ, ㅔ, ㅖ, ㅝ, ㅟ, ㅞ, ㅡ, ㅣ, ㅢ. Although there's an opinion that "ㅣ" is a neutral vowel, I see it as a dark one. Also it sounds like you're slightly, subtly insisting that he's handsome as compared to the first. 잘생긴 오빠 a handsome guy 킹카 a hunk

멋있어 ~ 멋지다 ~ 킹카 ~