What historical period and country interests you?
Some suggestions (that are not romance in disguise):
Edit: I just realised you still wanted a love story....
Rose by Martin Cruz Smith
'Fingersmith' and 'Affinity' by Sarah Waters
Any book by Judith Merkle Riley except the last three - they're humour, it might not be what you are looking for?
'Possession' by Antonia Byatt
In the Company of the Courtesan by Sarah Dunant (BTW, even if there actually *is* half-naked woman on the cover (I just realised), it's not 'romance', so don't diss it bec. of the cover
edit, added: 'Girl with a pearl earring' by Tracy Chevalier
Moved these out of the way. Good historical novels, but not love stories:
Colleen McColloughs 'Master's of Rome' series
Roanoke by Margaret Lawrence
Lempriere's Dictionary by Lawrence Norfolk
'A Conspiracy of Paper' and 'The Coffee Trader' by David Liss
The Blood Doctor by Barbara Vine
The Crimson Petal and the White by Michael Faber
The Physician by Noah Gordon