You are assuming that the deal never materialised because of NM and his Agent being BTC's.
Yet according to Richard Cadette, the Agent at least was eventually satisfied.
Now maybe NM on his own decided that he could get better elsewhere, and so turned you down?
But here's a more plausible explanation. The Agent started touting NM around some time back and realised SU were in the market for a striker. He spoke to you, saw you were v.interested, briefly overplayed his own hand (commission), but backed off so as not to scupper the deal. Terms were agreed between SU, player and agent.
SU then spoke to BFC, who were asking more than you were hoping/expecting/prepared to pay. In the end, CW would not go over his limit, as is his usual modus operandi, BFC would not go below it, as is ours, and so SU declined to lodge a bid (no point).
Which was the real reason NM's head wasn't in the right place: his best (only?) chance of getting his move to the PL this window now looked like foundering, because neither BFC or SU would budge.
"C'est la vie", comme disent les Français...