To first start dating any bachelorettes you must get her to at least 7 hearts. After you have done this you can ask her out while your talking to her with L or R on your Nintendo DS. Even though you can take her with you into dungeons before you get her to 7 hearts you still cannot take her on a date. You also can't be on a request. To activate a date you must walk into one of the date locations, Vale: Icy Rosebush, Sol Terrano: Star Dunes, Privera: Flower Field and Oddward: Rainbow Falls. Each of the bachelorettes have a favorite location to go on dates. She will say when you ask her out. Each area has a different dialog. After you get married it will be the same though.
To get married you must have the bachelorette at 10 hearts, have united the town and the Univir, have to have the double bed (purchased from Diamond General Store) and complete all of her requests. After you have done this Wells and Marjorie will show up and and give you the engagement ring's recipe for the Workshop. People who have played Rune Factory 2 might recognize this ring as Mana's proposal item. The recommended level for crafting this item is 20 and you will need 2 Silvers and a Ruby. To get the double bed, you need to defeat the twins monster at Oddward.