You H wants the divorce now because he is caught up with an OW - and is on a new high... That high will not last - just like it didn't with your OM.
The whole separation/divorce is a long rollercoaster ride of emotions. I'd focus on re-building yourself and be happy for yourself... and focus on your three children and what is right for them.
I would try to slow it down and collect your thoughts. Freeze the divorce is you wish. Let H do it if he is so anxious.
No one said a divorce has to be quick - it is likely the biggest decisions of your life and will have the largest impact on your and your children's future - what ever you do, do thoughtfully and not emotionally.
Me:40 / W:33 / D:3 T:7.5/M:4 D Day: 1/24/08 Legal Separated: 6/12/08 BF who sleeps over: confirmed 11/10/08 Suspect BF pre-dates D Day