"너 웃으면 나도 웃게 너 울으면 나도 울게 그래서, 혼자 느낌을 생각하지마 난 니 옆에 있잖아 영원히 사랑할게" I think this is what you meant. 너 웃으면 나도 웃을게 너 울면 나도 울게 그러니 혼자란 생각(은/을) 하지 마 (or 혼자란 느낌(을) 갖지 마 - not as natural) 난 네 옆에 있잖아 영원히 사랑할게 * 웃다 -> 웃으면, 웃을게, 웃을 거야, ... * 울다 -> 울면, 울게, 울 거야, ... * if you're not sure of a conjugated form, type in the root form (웃다) at "dongsa.net" to see all the conjugations (~(ㄹ/을)게 ending follows the ~(ㄹ/을) 거야 form). * 그래서 is usually used following a concrete action or event. * When just an intention or plan precedes it like here, 그러니(까) is more appropriate. * ~생각을 하다: think something; have a certain thought. * ~느낌을 생각하다 is like "think of some feeling" - doesn't make sense. * In writing the only acceptable adjective form of 너 is "네". * In conversation, it is often pronounced as 니.

너가 웃으면 나도 웃을게 너거 울면 나도 울게 그러니까 혼자라고 생각하지마 내가 니 옆에 있잖아 영원히 사랑할게 ♡ This would sound much better and native. Good day

네가 웃으면 나도 웃을게. (There needs to be post position after the pronoun / '너'+'가'= '네가' / '웃을게' : When you mean to say "I will do sth", it makes 'L(ㄹ)' sound on the stem. As for '웃다', the stem finished with consonant on the bottom, so you add on '을' between each one. ANOTHER EXAMPLES: 할게[하다], 갈게[가다], 올게[오다], 앉을게[앉다] etc.) 네가 울면 나도 울게. (Same with last sentence : '네가') 그러니까 혼자라고 생각하지마. (When you advise or console someone, we use '그러니(까)' for saying "so". + Even grammatically, '~하지마' isn't used with '그래서') 내가 네 옆에 있잖아. ('난'= '나는', but unnatural for this phrase. That is used when you explain about yourself of your behaviors / '니' isn't correct) 영원히 사랑할게 ♡