I feel same ;;
I didn't get that impression at all, because his "secret" was that he was in denial about being gay all along.
I don't think he actually asked her for her hand in marriage, but he was thinking about it, because he wanted to take care of the both of them (Shouta and Mami). Towards the end, he said that he didn't really know what a family felt like. My guess is that he probably wanted Mami and Shouta to have a proper family since Mami's family situation was complicated.
It just feels like he had more love towards Mami, even though he basically told Mami that he liked Hoshino...
Mami is an amazing person, but it's so hard to ship Akihiro and Hoshino after finding out Aki asked for Mami's hand in marriage.
Sigh... :/
SHOUTA IS ADORABLE THOUGH