Coupling solution
by Kegler
The 14 squares each contain a U from one direction and a P from the other, so, per 29 Across, you're "pairing" UP.
Across
| 1 | CAM(OUr + FLAG)E |
| 9 | LUGe |
| 12 | AL + O + HA |
| 13 | FACE (CAFE anag) |
| 14 | L(E)AP |
| 15 | MODELS (SELDOM anag) |
| 16 | SEA ("SEE" hom) |
| 17 | S(U)IT |
| 18 | COP + I + LOT |
| 19 | sURGING |
| 21 | P(EG + BO)ARD |
| 25 | ROO(S)T |
| 26 | IRISh |
| 27 | OPT (hidden) |
| 29 | PAIRING UP |
| 30 | lEaRnEr |
| 31 | STET (TEST anag) |
| 32 | UNT + IE (NUT anag) |
| 33 | RET(H)READ |
| 35 | SPA(S,M)S |
| 37 | TAN + T + RUM |
| 38 | Y + ENS |
| 40 | PAR (1st letters) |
| 42 | S(AT)IRE |
| 43 | ORDO (DOOR anag) |
| 44 | T + RAM |
| 45 | MISER (hidden) |
| 46 | PSI ("SIGH" hom) |
| 47 | D(EBUT)ANTES (TUBE rev) |
|
Down
| 1 | CAM(CORD)ER (CREAM anag) |
| 2 | A + LOOF (FOOL rev) |
| 3 | MODUS OPERANDI (AND IMPOSED OUR anag) |
| 4 | PAL + LET |
| 5 | LAST (hidden) |
| 6 | rACEs |
| 7 | GEAR (last letters) |
| 8 | ELS (2 defs) |
| 9 | LEPIDOPTERIST (I SPOTTED PERIL anag) |
| 10 | PAINFUL (UP FINAL anag) |
| 11 | GUT (rev) |
| 19 | PO(IN + T)E |
| 20 | G + ROUND |
| 21 | U(SAGE)S |
| 22 | G + RITHS (SHIRT anag) |
| 23 | BRIE + R |
| 24 | ST(R)EAMERS |
| 28 | ARGUERS (RUGS ARE anag) |
| 32 | P(AN + AM)A |
| 34 | SPREE (PEERS anag) |
| 36 | MUTE (rev hidden) |
| 37 | TRAP (rev) |
| 38 | YOU ("YEW" hom) |
| 39 | SODa |
| 41 | A + R + B |
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