Couple things -
And I'll preface this by saying that I think you're leaving something out... from the blowjob to the silent SPAM there's a step missing... So maybe you can fill in the blank.
Here's my assessment:
1) I think the reality of the situation may have hit her and that she's been blowing her brother's friend. There's no good ending to that story... Maybe she's being proactive; because:
2) She sure doesn't sound into it anymore (and that may be due to #1), or may be something else entirely. Maybe she's seeing someone else, maybe she's interested in someone else... Maybe you should have showered before she went down on you
My advice: Back-burner her and have other women as options. Keep pushing her when she's saying 'no' repeatedly and you're just asking for an awkward situation (plus you look desperate).