Without being at all familiar with The Tenant of Wildfell Hall, I agree that Henry's good behaviour as Fanny's husband would be a precarious thing. He has an established liking to make girls a little in love with him (according to his sister in ch36). If he doesn't give that up, there's still a distinct possibility that he'd respond to Maria's coldness with a new bout of flirtation. His marriage might be enough to put Maria off from attempting a 'man upgrade'; then, perhaps, she'd remain resentful and his taste for flirtation would flit off to someone else.

So, might he give up his taste for flirtation? I don't see any precedent for it. He's already come out and said "... I never do wrong without gaining by it ..." (ch25), which makes it sound like he has no experience in dealing with loss or disappointment**. He's a little acquainted with self-denial, but still regards it as a curious novelty: A little difficulty to be overcome was no evil to Henry Crawford. He rather derived spirits from it. He had been apt to gain hearts too easily. His situation was new and animating. (ch33). Novelties tend to wear off, though. It's all left hinging on whether he could have found sufficient exultation in overcoming the reluctance, in working himself into the esteem and tenderness of Fanny Price (ch48).