I agree with maths.
Something I found, and have noticed in others on longer term threads, is that at the start all the focus is on the details of the affair itself. You may discuss the reasons, but you aren't thinking so clearly.
As the dust settles, after 2-3 months, and especially if it wasn't satisfactorily bottomed out, many people start to see the connection between the affair and other general patterns in the marriage.
For example, some get to the bottom of old niggles in new ways. Some see a general pattern of selfishness in the unfaithful parties behaviour over the years which they had suppressed or ignored.
Especially if the man promises more changes than he really prepared to make ( or vice versa, if a woman). Many people have real trouble actually understanding what needs to happen and that the change is permanent.
Eg- and I am only conjecturing here- maybe your h has trouble being the person who offers support rather than receives it, in which case he may subconsciously see himself as entitled to what he did. Or perhaps he felt that support is a short term offer, rather than a sustained effort.