Sounds like your h is experiencing a "quarter life crisis". We all go through something in the teens, early 20's, etc. However, if we don't navigate those quarter life transitions properly, many will have a midlife crisis later on in life.
A year isn't very long when it comes to life transitions. It could take a while before your h finally settles back down into his routine. I know it sounds like a long time to you, but it's only a blip on the radar screen for him, i.e., his clock is moving at a turtle's pace for him. So, while he's out there acting like a teen, you will need to work on you, change the things that you know need to be changed (only do them for you and you have to make them permanent or he'll know you only did it get him back), focus on your children and your life as it is right now. Do not try to force him out of his crisis...just leave him alone as much as possible, i.e., contact him only in an emergency or something to do w/the children.
Live your life to the fullest and continue moving forward. BTW, if you begin dating, you are sending him a clear signal that it's okay that he's out there doing his thing and possibly dating and/or having the ow live w/him and it also alleviates any guilt he may have for doing so. Also, you do not want to get involved w/another person because what happens if your h suddenly decides to return and your current "date" has some serious feelings for you and vice versa? It's best to leave dating alone for just a bit and focus on your healing and when the time is right, you'll be able to move forward and enjoy the company of another person. Right now, you are still spinning from what your h has done and you do not want to have that elephant in the room when you do start dating. Wait a bit...there's no hurry to "mirror" what he's doing out there right now. Learn to be comfortable w/your own company and enjoy exploring the new and improved you for a bit.
Just my two cents.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.