Harry realizes he has a problem. As he continues through his teen years and magical maturation his magic is evolving differently that his friends. Harry is developing a high degree of proficiency with fire based spells, emotion based spells, and his body is developing faster with significant increases to strength and a (quite frankly) ridiculously increased natural healing.
It's all his Harry 'Plot-Device' Potter's normal reaction to having phoenix tears circulating in his body and magic during his maturity.
Fourth year rolls up and after encountering the Veela at the world cup Harry reacts, but not like the rest of the boys do, he feels 'home' and 'safety' and 'nesting'.
Triwizard tournament Harry's attention is drawn to Fleur since he can practically feel the fire in her magic that calls to him. Fleur can hear him as well but his call to her is muted and smothered.
Harry takes an AK to the face in 7th year and after awakening and defeating Specter-Mort Harry's bond with his phoenix magic fully begins to grow unimpeded by the horcrux. Harry, who wants to avoid Fleur (who is married to Bill or engaged, whatever works best for the story) because he reacts to her Veela allure much more strongly than others, contacts Appolline and gets a meeting with Grandmere Delacour and is tentatively invited to the French Veela conclave to learn about the allure while also being able to experiment with the extent of his now natural phoenix magics and how they relate similarly to Veela.
Grandmere teases Fleur in a letter that she let such an interesting young man out of her grasp and eventually Fleur (takes a trip while her husband is working with Gringotts or breaks up with her fiancee due to changes in personality after the final battle) comes to visit learning that her grandmother has her her claws in Harry Potter.
Insert hilarious relationship shenanigans. And fire cuz Phoenix and Veela.