Glad you're enjoying it!
Lone Rogue is the "default" ending if you aren't dating anyone. The four dateable guys will all ask you out by mid-October, so if you've hit late October and are still single, you will be for the rest of the game.
Carlos should be easy to date if you spend as much time with him as possible, but that also means you can't get on Adam's bad side early (for example, by snooping on his computer or giving him the impression that you don't like frat guys).
Let me know if you're still having trouble. He should ask you out on October 3, if he likes you enough by then.