They don't have to be gay though. There's also that thing called bisexuality. None of them has ever liked a man before, so it's pretty damn obvious they're confused.
I understand that and it's why it's so important that they talk, how long this confusion is gonna take. If they are gay, bi or even pan, I think the author is leaving this things aside only to show more and more sex scenes, and I don't know the story was so interest in the beggining now all the latest chapters seem the same. （￣へ￣）
Sometimes you just don't realise your feelings right away, you know... And we don't even know for how long it's been like this, time period is not really specified, so we don't know if it's been for weeks, for months or what.
Sure they should talk, but I don't think currently they're experiencing comnunication problems except for that misunderstanding in the beginning. They just haven't come to terms with their own feelings yet.
I really like this manga, but the lack of sincerity between the two caracters makes me think how long this gonna take, please author they have sex every time they meet and still don't know what they feel? At least some real conversation they need to have, because it's not clear for them that they're gay? That they like each other? (yes, I'm a little angry because I want things between them to go further) （￣へ￣）