If you are new to this site, and especially if your spouse has a foot out the door--start with Newcomers, at least initially, to learn the basic techniques/skills. You will also want to check out the Divorce Remedy forum. Then:
If you are dealing with the specific issue of Infidelity, you might like to check out that forum.
If you are having trouble with a SEX-STARVED MARRIAGE, you may also like to find some support and creative solutions on that forum.
When your spouse is really willing to work with you, and has stopped talking about leaving, you are PIECING. I'll explain later, but it's important to catch that step and act accordingly. This is the space in which to really build your skill set and strengthen your relationship. You may find you backslide here, that's OK. Pick yourself up, dust yourself off--you're still 'Piecing' unless you really want to join a different forum. There is no need to go back to newcomers. You just begin again with a 'Beginner's Mind' if you need to.
Later, when you feel you are on more solid ground or that you have advanced, we have a forum for you if you'd still like to work on your DB skill set and get support: After Reconciling--Keeping the Changes Going.
We have other forums that you may want to check out, but this is the 'nuts and bolts'.