The best way to get off the roller coaster is to detach...
There's many ways to help, plus the support on the board.
Do you have the DR book? It goes through a lot of the actual mechanisms to help you work through this horrible time.
And, the infidelity forum is great for support specifically related to infidelity, but as Seeking_Answers indicated, weekends can be slow and sub forums like this can also be slow.
If you want more active support at this early stage, you may want to post in the "Newcomers" forum.
Get yourself grounded. Remember that you came here because you obviously want to or would like to consider saving your M (which is what this is all about) and that there are plenty of Ms that have survived infidelity and have subsequently thrived.
We go through a process of detaching, GALing, 180s, and just having the support of pro-M people, like on this board.
