Advice Needed- setting boundaries

[Sam3]

Hi, I'm new here. I'm about halfway thru DR book. I have been trying to implement the 37 rules. My story is - My husband took a job 2 years ago, that is 3 hours from home. He works mon- thurs, mon- fri alternating weeks. He comes either Thurs or Fri thru Min morning. I had a baby #3 on 2/20. Pregnancy was a bit of a suprise. Thought we were going with "if it happens, it happens". Husband was not happy when pregnancy was confirmed. I thought it was a bit of shock in how life was going to change since we were just getting out of infant/toddler stage with other 2 kids and life was getting easier. We both agreed it would all work out. Baby was born very sick and almost died. He spent his first 29 days in the Nicu. We finally brought him home end of March. Life has continued on husband still works out of town. Has more responsibilities with other kids since I am busy with newborn & he has some special medical needs.

Thought things were getting better. On Mothers Day, husband says he is having a hard time connecting with Baby #3. Because so much of his medical care - I do. Says he is really missing his kids. Having a hard time being away from us. I assure him things will be back to a new normal soon as its a shift in our family dynamics for everyone.
He complains that I haven't been keeping up with grocery shopping & meal planning and he has been doing own laundry. I let him know I'm doing my best & will try to get everything back to normal.

He continues to call every day, saying he loves me, misses us etc.
On may 23- before I big kids go to bed, he gets a shower, gets dressed and says he is going out. I was like "what?" He tells me ILYBNILWY, that he needs space, he is lonely, but he feels his life is now in city where he works and wants to go do his own thing for a while. I was completely shocked. He said he knows he should be happy that baby is doing so well - but he just doesn't feel it. Says he feels unloved, I don't initiate intimacy etc.
That weekend he went out fri, sat & sun night with friends.
Sunday night I went thru his phone (something I've never done) and discovered he downloaded a secret folder app that holds texts & calls.
I also see that he has several texts from a from a friend if his that just don't make sense. So I look at the contact info for the name & it's a different phone number. I do a cell reverse lookup & it is a girls number. In my investigating I have found out she is a bartender at a restaurant that he goes to frequently. The texts are taking place at all hours while he is home on weekend with us. The oldest was from the 5/16.
I asked him if there was someone else- he says he is not in a relationship with anyone, doesn't want to be in relationship with anyone including me. I ask him if in taking his space can he stay committed to our marriage? He says no. He tells me if he figured things out in 6 months & I'm here great. But if I'm not -I'm not. That would be his bad.

He tells me he is still going to come home on weekends to spend time with kids. Nothing is changing there except our relationship is over. I went to a marriage counselor that we saw 4 years ago after baby #2. Husband went in one time & had a phone session once.
Counselor says husband is prob having mid life crisis & I should fight for my marriage.

I have not confronted husband with information about other woman. I don't know how & feel I need more proof so he doesn't dismiss me & say she's a friend.
More background- we have no boundaries. He had always done whatever he wants to do. I've always let him do his own thing & hang out with friends whenever he wanted.
I am a stay at home mom. He has his own bank accounts that his check is direct deposited into. He gives me a weekly check from him for me to pay for household expenses- groceries, diapers, clothes for kids etc.
I'm concerned that if he does want divorce he could spend nearly everything he has in bank & leave me high & dry. I want to save my marriage, but dont want to be in a bad financial situation. We were in the process of building a second/vacation home closer to his job. Somewhere to spend some weekends & let kids ride atv's etc.
He told me he would continue to do everything the same for 6 months & once the other house is done, he will prob just stay there. I can't afford to keep this house.

He sent me a text on 5/29 saying that he wants to work things out eventually and that he does love me. I was cautious when he came home that weekend. On Saturday night if that weekend he went out & never came home until 11 am the next day. He said he stayed at his best friends house.
I'm having a hard time detaching with such young children. He wants to talk to them on the phone each day & them wants to talk to me about their day. I suggested i text him about their day, he said why cant you just tell me. But it's only on the days he feels like calling. He went on a fishing trip with some buddies 2 weeks ago and we didnt hear from him for 2 days. I have not initiated contact with him, I have been answering his questions about kids but not making chit chat. This week he calls & says I'm being short with him. I told him I'm a little confused and need to protect myself. My kids tried to call him the other night 4 times, I sent 2 text messages saying they wanted to say goodnight. I could see he was reading the text messages. He never responded. I asked him about it lady night when he got home & said kids were really missing him. He said he was at a concert & he couldn't talk.

I'm trying to be pleasant when I'm around him in person and have been leaving the house quite a bit to leave him at home with the older kids. Don't really want to be around him & it's quite exhausting to be "on" all the time. As I'm pretty exhausted having a newborn & taking care of other 2 kids all week by myself.
He is continuing to text OW each weekend while he is here.

My questions-
How do I GAL with a newborn with some special medical needs?
Do I ask or confront about OW? The issues with our marriage are now bigger than what he initially presented.
How to set some boundaries with someone who has never had any?
How to limit contact but encourage communication with older kids who literally count down the days each week until he comes home?
How to detach with 3 small children?

I feel like he is rolling over all of us right now. He does whatever he wants including talking to kids when he feels like it.
Sorry this is long. Advice is needed! Please.