Whether you separate to stay depends on how you feel, and you should probably sit and think about it for awhile, although maybe you already have.
I think your H suddenly realizes that you are not the sure thing, and this explains his recent behavior. He CAN lose you, and this is the first time it seems real to him. However, I do not think it is the end of the MLC and his behavior. Once he thinks your safe again, he may revert to his current ways.
You might delay separation and remain detached from H and see how your sitch progresses. Maybe even use the current sitch to set boundaries on him and OW?
