You also have to remember "friends-with-benefits".
In my opinion, there's a difference between being friends-with-benefits and fuck buddies. Currently, I am in a weird situation in that I feel we are moving beyond the friends-with-benefits deal (due to meeting her mother, and having to go out and have no sex), but neither of us have said anything about exclusivity, and the only times I talk to her on the phone is when she is calling me to tell me she is coming over, or vice versa. Longest convo has been 2-3 minutes. This is in nearly 4 months of fucking around. We do text and IM or whatever.
Fuck buddies don't really hang out, they may text/call each other when they're down town to see what's up and see if they want to meet up later. Pretty much synonymous with a "booty call". Limited contact with each other when not having sex.
Obviously if the dude is buying you shit, taking you to dinner, and peppering you with terms like "sweetie" or "honey" instead of "cum dumpster" or telling you to "swallow my throat yogurt", then he's probably looking for something a little more serious - a little more deeper. I have not taken my girl out to dinner per se, but we have gone out for gelato, and wine and cheese, and she ate some of my macaroni and cheese while we were watching a movie at this theater here called the Alamo Drafthouse that serves booze and food. To me, when I take her to dinner, that's a sign I want to be more romantically involved. It's probably a sign to her too, since we haven't ever gone to dinner. She'll get it.
So I guess what I'm saying is if he does something differently than he has been doing - for instance taking you out to dinner (you may already have been going out for dinner, then it would have to be something else that's "different"), he's probably lookin' to step it up.
your dad fucked your brother