The movie is romantic comedy from 90's, I think. Propably made in USA.
Some guy, dumped by his gf is dating other girls. First part of movie shows hilarious, failed dates with many girls. After that he talks with friends about his past, when he met some girl on the airport. He gave her his address, but she throwed it into garbage. Her younger sister picked it up and started to write letters with him. They were writing about their love and possible future together. After few weeks her parents found letters and call a police, so the guy is charged as a pedophile, lol (he didn't know he was writing with younger sister). This story looks like a side plot, the guy but in the end the guy met this young girl during his friend wedding and it's happy and of whole story.