Al and May
Alphonse's relationship with May for most of the series is a one-sided crush, with her doting and lavishing praises on him while he seems to see her as no more than a friend and ally. However, his chivalrous and protective nature ensures that he takes on the task of her protection during their battles together. Her sudden attraction to Al is initially based on his own description of his human body in contrast to the appearance of his older brother. Al's interest in her appears to be largely intellectual, at least at first, as he hopes to learn alkahestry from her. However, their adventures in the North seem to have been leading towards a closer relationship, as each recognized in the other an intellectual equal. At the end of the series, Alphonse ventures to Xing to study alkahestry under May's tutelage and returns with her to Amestris some time later. Years later, she is featured in the Elric family photo next to Al, implying she and Alphonse have deepened their relationship over time.