Why would he want to "get the girl?" He can't afford to marry a poor girl like Marianne, so the last thing he wants is ot "get her" - unless you mean that he wanted to seduce her which I think would be unthinkable. Im sure if all Will wanted was to get rid of an expensive horse, he could sell it, and at least make some money on it, even if not as much as he might like.. rather than just give it away. I think he gave it because he does like Marianne and wants to make her happy by the gift and it means they can go riding togehter at times.