My advice is to break off all contact with OM. And completely give you and your husband time to focus and work on your marriage. You have to give it your best shot by being kind, compassionate and loyal to each other. If you work on your marriage at least if you do decide in the future to split up, you know that you have tried your best. And you won't look back with regret and longing for your old comfortable life.
Your husband probably feels very comfortable and familiar, and he is your best friend. This is because you two have a lot of history together, you have lived with each other for so long. You have washed his underpants and paired his socks etc.
The OM is more of a heady fantasy kind of relationship, which is a hell of a lot more exciting. The relationship is run on secrecy which only fuels intimacy and sexual chemistry which in turn heightens that feeling of a special connection and desire. Its all a fallacy. If you did leave your H, and set up home with the OM, he too would eventually become your best friend and life would be humdrum, and you may again seek to escape and recreate that exciting feeling with someone new.
And lets face it, your relationship is based on lies, deceit and betrayal of trust. He may not always be able to trust you, nor you him.
Search in your heart. When you first became attracted to the OM, you must have suppressed your feelings for your H, in order to focus and concentrate on the OM? And then did you begin to concentrate on negative feelings about your H in order to justify your affair with OM? As you distanced yourself from your H, as you became further embroiled in the affair?
You can reverse this, by building walls between you and OM (stop seeing him and stop interacting with him). And re focussing all your energy and time on your H. By being kind, compassionate and loyal. By spending time together alone and with your dcs. By appreciating that he is your best friend and working on recreating more intimate and intense feelings for him again. That you have repressed up to now.
If you do break your marriage up, you will cause untold pain and confusion. Its not worth it.
Your children and marriage should come first. Think of them and the fact that you can work on your marriage and improve things.
If you are kind and compassionate to your H, he will reflect this to you!!
Good luck. I hope you think long and hard about your future. And don't start a new relationship based on the shaky ground of lies and deceit.