All things now considered its best you find a way to establish some clear defined boundaries with H.
Stop the coming and going at his desire.
He wants to do laundry - there's a thing called launder-mat. He wants to have kids for dinner he can cook at his apartment or take them out. Wants family dinner? Then he can take you all out but remember you might want to let him know you are busy.
Gee - what if he starts doing laundry at OW's? Let him. Most A's eventually fizzle out because real life sets in - let her see what an arse he can be if he gets grumpy about doing his own laundry. If you haven't already read His Needs/Her Needs - How to Affair Proof Your Marriage. Right now the A is filling one need but once you start relying on the A to fill all your needs they start seeing all the flaws.
In the meantime keep up with GAL. It will help you figure out what you are capable of and what you are capable of living with. You've been down this road before - what if you fix things again and he does this again in another 10yr. Will it be worth it? I'm not judging because maybe it is but you certainly have a pattern that requires your attention.
Certainly don't take the steps to enable the D but don't put up with being treated like a doormat. Get your ducks in row as they say.
I still highly encourage you to read Love Must Be Tough. Now I wasn't into all the religious aspects but it was still a good read and helpful.
I have no doubt that H mentioning he wanted to date others WAS his way of telling you about OW.
There is always a point when couples separate that they come to agreements. Sometimes couples agree not to date or involve others during this time and other couples agree that its an option. The most important part is that the couple discusses their expectations of a separation and sometimes even draft a contract - see Controlled Separation.
Your H has been guilty of an A before and how did that resolve? Did the A fizzle out or did he actually choose to come home to his wife? Were you clear about future expectation in regards to your R? Did you ever let him know that you would not tolerate another A? I'm just wondering why your H would feel you would tolerate him dating others while still M?
Meg you can do this - None of here knows what is going to happen with your M but you can get through this and find out you are so much stronger than you feel you are. Stop beating yourself up - most woman neglect their H to some degree in regards to kids. It happens. Many H's are needy little creatures - almost like another child. NOW-I'm not dissing all men or H's out there!!! I know my H is a very needy man. If I am meeting his needs in this he is an amazing H - but its easy to put him on the back burner because he is a grown adult. From you describe your H is most likely a very needy man as well. Read the book - it will help you... then its up to you to decide what it is that YOU want. Not your H.