Rabadash did plan to capture Susan and force her to marry him. How he feels about her is just twisted.
When he visited Cair Paravel, he seemed to be a nice guy. Even Susan was impressed. When Susan and Edmund visit Tashbaan, she began to have second thoughts about marrying Rabadash.
Then there's even a whole chapter about what he plans to do: conquer Archenland, then on to Cair Paravel, and capture Susan, and ride back to Anvard.
If Susan had marry Rabadash, well given how in the upper class society of Calormen, Rabadash would have been a controlling husband. Tisrocs, princes, and tarkaans have been known to treat their wives and daughters and possibly sisters as nothing more than property.
