I guess if you catch yourself writing out the romance, cut it out immediately. However, romance is popular among mainstream. There is Harry Potter where Harry Potter fights against Voldemort and, in the meanwhile, falls in and out of love with girls. There is the Hunger Games where Katniss is juggling with her abstract feelings for Peeta and her will to live. There is Misery where Annie Wilkes keeps Paul Sheldon, an author of one of her favourite books, is kept prisoner due to her (warped) love for both him and his books. It's a strong plot device that can be used in any way you wish; it depends on how you use it.
It seems to me that there are all sorts of personality characteristics that could allow friendship but prevent romance: - He doesn't want kids, or can't have kids, or has a genetic issue that means that he refuses to have kids. And her whole idea of romance revolves around marriage with kids. (Reversing the sexes works just fine, too - he wants kids, she doesn't.) This probably requires characters old enough to at least be thinking about marriage. - He has a traditional view of women as the passive sex, people who should be protected, be obedient, not go out in the wide world, And she doesn't buy into that one little bit. Again, you can reverse this - she wants to be protected and he wants someone independent. And this doesn't really require that the characters be older than teenagers. - He flits from girl to girl, and she can't feel the slightest romantic twinge unless she's confident that her guy is bonded to her and no one else. Again sex-reversible. I'm sure that there are lots more. And all of the above allow for sexual tension, while preventing a romance. Any of them could be resolved if you _wanted_ a romance, but that would require a lot of plot development and untangling, so you should be able to see trouble coming and suppress that untangling.
Awww, the title of this is cute. My advice is; make sure their romance isn't anything vital to the plot. If you really can't help it, then go ahead, write a little fluff here and there. Then, once you've written the story, create another word document and cut all of those fluffy parts out so you are left with the story that was meant to happen in one place and your fluff in another for your own personal viewing.
