Nintendo of Japan has made a statement on the matter, translated here
https://gonintendo.com/stories/340410-nintendo-shares-a-statement-with-japanese-audiences-on-the-same-s
"In Fire Emblem Three Houses, it is possible for the Protagonist to have same-sex relationships with certain characters. However, we cannot explain this topic in more detail as to not ruin the excitement of all users who are looking forward to it.
Regarding character raising, we have prepared a lot of options, so please kindly anticipate it."








