If you are a Japanese guy, you do not “suki” your friends. Girls have more freedom with this and can toss it around a bit more willy-nilly, but it’s not something you tell someone as a guy unless you’re pretty serious about them. (And even then, guys saying it is still pretty rare…
When you do a lover’s route with the girls in P4, their “I love you” at Rank 10 is a “suki”/”suki desu” in Japanese.
So despite the fact that “suki” can be used for inanimate objects/family/friends, Yosuke’s “
ore, omae ga suki da” (“I like you”
is unquestionably a lover’s route statement. He would not say this to Souji in a casual manner, because if he was just trying to convey feelings of friendship he probably would have said something more like “you’re important to me”.