Kodocha aka Kodomo no Omocha
The main characters are Akito Hayama and Sana Kurata.
Sana Kurata has a charmed life. Not only is her mother is a famous, award-winning writer, but she's the star of the hit TV comedy "Child's Toy" while still in the fifth grade. But Sana's biggest concern is Akito Hayama, a pint-sized hellion who's organized the boys in their grade-school class into a mass of unending noise and violence. With the help of Rei, her manager, chauffeur and "pimp," Sana is determined to win back control of the classroom from her new arch-enemy. But as her crusade continues, Sana moves further into Akito's life, and finds that he might not be entirely bad...or entirely safe.
There are about 50 or so chapters, its a pretty good read, I just finished reading it today. Unexpectedly i cried at 1 point in the manga (near the end)
Other mangas that i might recommend are:
Usotsuki Lily (romance shoujo, the male lead has a girlfriend but she doesnt like his crossdressing habits)
The One (romance josei, the main female strives to be a top model. I really liked this one)
Youth Gone Wild (Romance same mangaka as The One, but i havent finished it yet. Its about making a band)
Cat Street (Romance, a child actress now a teenager has become antisocial bcuz of an event that happened in her past. Its a story about her recovering and opening her heart back up again)
Ashita no Ousama (Romance female lead and her discovery of the joy of becoming a playwright.)
Penguin Revolution (Romance. Based around the acting business)
Skip Beat (shoujo romance, comedy. Also based on acting)
Glass mask (i actually didnt read the manga but i watched the 2005 anime remake, one of my top 10 fav anime's as of today. Revolves around acting. The main character is a diamond in the rough genius actress. Has romance but id say its 65% plot and 35% Romance, but even if u are just looking for romance i think you should watch this show cuz i absolutely loved it ^^)