Stories aren't exactly the same, but unrequited love is a major dynamic in both. Mysterious girl Appears in main male character's bedroom, a love triangle then forms, male lead tries to make the right decision about life and love. Only difference is that VGA does not lack an ending... lol
Both are tackling complicated relationships and the comedy that goes with it
Sakura Diaries is a little R+ rated and tackles a taboo subject. (but its okay if they're not related by blood right?)
Lovely Complex is more PG rated and is more conventional.
Both are still funny dramas in their own right. When i was watching Sakura Diaries i kept comparing it to Love Complex throughout the entire viewing.