The best implementation of intraparty romance I’ve ever seen is in the Dragon Age video game. Inspiring dialogue, decision points and elegant rules combine to create a wonderful model that can easily fit into your own D&D adventures, from whomever love or romance springs in your party.
NPC companion characters or party allies particularly make excellent potential romance options in D&D, whether they’re a good friend whose been with the crew since day one (perhaps filling out a small party and missing tactical roles in the process), or an unusual sort passing through for just an adventure with his or her goals temporarily or tangentially aligned with the rest of the party.
For example, maybe that lovely fire-haired lady is simply also headed for Winterhaven, and could both use and offer some company and protection along the way. Love and romance often begin in such incidental ways.