I'm surprised ths hasnt been posted for all to see in this community.
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One questions, I guess it been quite some time between the return in Resembool and the proposal athough there people say its a confession and others a proposal. The question I guess well how likely was it that they were already in a relationship before Ed proposal happened. It seem likely, by the way, the dialogue while Ed and Al were walking to the house. Ed tease Al about Mei and Al right back at him for Winry . The dialogue and Ed's face....., Ed " alphonse-kun, it sure looks like mei chan-sama, the princess of xing, likes you quite a bit" Al respond seemly in agreement "she's such a nice girl" and Al saying ".that aside, brother, are you sure about winry?" with Ed making a oooo face reaction until they pause and look at the house. Nice of the anime to add that.