well, what kind of adventure/romance are you looking for? what kind of female characters/male characters and other genres do you like? do you prefer shounen/shoujo? because I have a vast manga collection, mostly shoujo, and if you really need a recommendation, just give me a bit more info and I can come up with the perfect one, or tell me a series you're thinking about and I'll give you the lowdown on whether its worth it or not ^_^ oh, and how much romance do you need? do you want the focus to be on the adventure part more, or the romance?
man, I get really into questions like these lol I agree with others that "Inu-yasha" is good for romance/adventure, but there are so many volumes and the latest ones drag on, so you might not want to invest in that..."fullmetal alchemist" has a bit of romance, but is more about adventure...but it's also a good overall drama and has little moments of comedy within; its pretty well rounded. "fruits basket" would qualify as an adventure I suppose, if you consider curses and people changing into animals of the zodiac and a freaky head of house god type person adventure @_@ and its a good one for frustrating romances as well *(^_^)*