In my experience, if you drop talking about a plan to improve the marriage, such as going to a MC or going to a Retrouvaille weekend (and there are a lot of summer weekends out there this month and next), then nothing happens. To get change, you have to make change. And the opposite is also true, if nothing changes, then everything stays the same. And if everything stays the same, then this time period of goodwill is likely to wear off and you go back to where you were before. Some say that a happy marriage is falling in love with the same person over and over again. That is because the "in love" feeling does not just last.
You are no longer in the affair stage of this relationship, you are now in the piecing phase. You don't act the same in piecing as you do in trying to end an affair. You do have to take steps to heal the marriage, more than just day-to-day getting along. Because things will happen and you will lapse into old patterns. You need to actively change the patterns in a determined way, preferably led by someone who has experience doing this successfully.
