Nichiyoubi wa Issho ni

This is the story of three girls who all realize that the boys they've been chasing aren't available at the same time, and so decide to meet on a Sunday to invite the first boys they see to a party they're going to put together. Of course, it's not anywhere near that simple, and the three boys/men they pick up are all connected although none of them are aware of it, and some events in their own lives are going to complicate things...

(Source: M-U)