In this period piece on female independence, Bathsheba begins by breaking the mold of women in her time; she is a badass, independent, awesome. But as three significant men are introduced into her life, her insecurity is exposed.
She rejects Mr. Oak because she does not want to be a man's property (understandable). However, once she makes a name for herself, things start to change and doubt creeps in. She pushes Oak away with repeated excuses of not wanting a man to judge her, own her, or belittle her. However, Oak is the only man throughout the film to do none of these things. He points out that pranking Boldwood (a future suitor) with a joke valentine is beneath her. This may seem like a judgment, but in reality it is merely a fact, as her initial gut told her not to do that because he wouldn't see the humor, but she did it anyway. When Oak metaphorically holds a mirror to her face, she lashes out at him. She continually projects her own insecurities and self-doubts onto Mr. Oak.
Later, when Boldwood proposes, she initially rejects him but then at the last second gives him hope that she will think about it. I believe that she rejected him because, like Oak's first proposal, he makes it seem like she will be an ornament in the house. Then, in his second proposal, he says that her prosperous farm will be simply a hobby once they are married and he provides shelter and comfort, etc. Still, the fact that she led him on for months on end is cruel. Granted, she wasn't 100% sure, but again, her gut reaction was to say no and again she didn't follow it.
The man she actually marries in the film, Sergeant Troy, is the other extreme.
Initially he seems very lenient. He does not attempt to change her outright and yet subtly plays with her emotions. He slowly and quite randomly tries to take over the farm, giving Oak directions despite her objections. He also gambles away the farm's money, leaving her in debt. The fact that she marries him is extremely out of character. Throughout the whole film, she repeatedly claims she doesn't need a husband and turns down two proposals. Once this charming sweet-talker Sgt. Troy shows up, all of that flies out the window. He plays on her insecurities by talking about a beautiful woman he once was in love with (Fanny Robbin). This makes her jealous and, as she claims later in the film, she marries him out of jealousy and distraction.
These experiences, however, are what guide her into realizing that Oak is actually the perfect man for her. He loves her and wants to take care of her without stifling her. She learns that a husband does not have to be a negative concept; a woman is no less a woman with a man by her side, supporting her and mutually enhancing each others' lives.
(Although we all know Old George is ultimately the best choice!)