Help dealing with husband in another emotional affair (most likely)

There is a friend, of ours that's in our old west reenactment group my husband: Mike and I are members of that we both got along with and enjoyed hanging out with.
Her name is “Barb” I liked her because I used to think she was a lot like me . She was lot of fun to be around. We have a few things in common such as horses and trail riding the way we are.
My husband makes friends easily with anyone and everyone, Where as I do not have a ton of friends ans takes longer to get to know someone. let alone many female friends that I have things in common with.

We are about to go on a weeklong horse camping trip with “Barb”, but due to recent events that have come up more and more in the last year or so, I'm not sure I want her to go with us because of how close my husband and Barb are.
The reason the two of them are closer than all 3 of us is that within the last year I quit gong to our old west group. Barb still goes to perform in our group every 3 weekends in the various skits with Mike and the rest of our group
Sometimes Mike leaves home around 10:30 with his horse which he uses in the shows. He and Barb will meet early and go ride around the area,, then the rest of our old west group shows up and pitches in to help set up for the show .

Barb used to be close buddies with another (older) married man in our old west group ( named Lloyd) who has a horse that he uses in our shows and he too was into trail riding. Up till last year all 3 of them used to do a lot together.
They liked to go to a 3 day horse event.that includes demos and symposiums.

Since we moved I didn't want to go anymore, so I told Mike he may as well go with his friend Lloyd and Barb for the day to the horse event..
They would all meet for breakfast somewhere and then drive together in Mikes truck the horse show, spend the day there then come back home that night.
I
'd hear about how much Barb cracked joked around with them etc and how they all had a lot of fun. I felt like I was missing out yet I still did not want to go spend all day there being bored watching various horse demos etc.

In addition to all that, a year ago Mike became the president of our old west group and Barb became the V.P. they talk quite often on his cell phone regarding group/board issues that come up as well as laughing and joking around constantly.
I made it clear a long time ago about how this bothered me all the laughing and joking around he was doing with her and how close they seemed to be getting.

When I asked Barb & Mike at different times why she only calls his cell each of them said she does not have our home number on her cell.
Which of course I know is BS since she knows our home number but never bothered to put it on her cell phone since she uses her cell only .

Of course he always acts as if it is no big deal. Stating that the calls are nothing more than Barb just needs to blow off steam and talk to someone about work or whatever else is bothering her in her personal life etc.
Then the calls/conversations seemed to increase after she separated several months ago from her husband, and she's been confiding in Mike about all that.
I know because Mike would tell me how Barb was having a tough time with whatever and he'd tell me not to tell anyone about it because she did not want people in our group to find out about it..
Just the other day when I forgot and made the mistake of asking her something about her divorce , Mike overheard me and after we got in our car to go home, he jumped on my case saying "Why did you do that?! I told you no one was supposed to know about that!
he added that he was not going to tell me anything that she told him anymore. That is what pissed me off big time. I know that he does not tell me everything all the time as is that the two of them talk about..
It made I think about how she was using him to confide all her problems and secretes. whatnot.
Even when I've commented on how Barb calls him a lot and ask him what did she wanted that time? He would say that she does not call that often, and say oh you know Barb, she was talking a mile a minute about work and stuff. I just was listening.
Yet from my end I would see him laughing loudly and joking around the way they've done for the past 2 or so years.
The more I thought about it, the more I thought why is another woman confiding in my husband about her personal problems and then telling him not to tell me. I can only assume based on his strong reaction to me casually asking how she was doing with the divorce etc, that she must have told him not to tell even me( his wife)
Or else why would it be a big deal that I had talked to her about that?

To me if things were so innocent between them the way Mike claims, then he should not be allowing anther women to confide in him when no one else is around then tell him not to tell even me about it. And not go on with the whole “ we're just friends and I am “just listening to her talk” etc.
Anyway after I told him again that I did not like how close they've become and she talks to him about her problems and he got mad at me for saying anything to her about it( because no one was supposed to know) He got defensive and said what do you want me to to do? not be friends?! It was a tactic he's used before whenever I've expressed my concerns about how close a women is getting to him.
Every time I find a female that I can be friends with and they meet Mike( being the what they think is a fun/nice guy to talk to) as soon as that person needs someone to talk to, Mike is the one they turn to because" he is such a good listener".
Inevitably after they get to confide in him about their problems he feels good about being there for them and of course that leads into him getting too close to them and compromising our marriage.
Barb and Mike are that way and although I do not suspect him of having a physical affaire, he is too emotionally involved with this girl. I do not like it that once again he is close to another woman who is confiding in him and I'm not supposed know what she told him.
Or the fact about how often they hang out even tho mike would like me to buy his crap about how he does not see her that much. ( which was another argument we had regarding how I didn't like him laughing and joking with her on the phone all the time or or how she only confides in him etc every time they are at our old west shows.
I really liked this girl because she and I had a lot in common . So I am mad that she's now messed things up by picking my husband to confide in and leave me out of the loop. And expect him not to tell me.
Should I deal with Barb and tell her I do not like how close they've become and I do not want her calling him on his cell?
How I do not like that she only calls him even when it involves Mike and I.
So far I've only delt with Mike and said that I do not want him hanging out with her anymore and or talking to her in person or on his cell phone anymore. Yet I know he will see her at our old west shows every Sat when I am not there to watch him.

I felt better that I finally told Mike I am not comfortable with Barb going with us on this horse camping trip, because of how close they've become. Even though he argued with me claiming their friendship is not anything more than that etc.
He got very defensive then angrily said he would cut off all communication with her just to make me happy.
Yet given his past history with cheating ( at least 3 times within the last 3 years) I am sure he may be texting her and then deleting the messages. I have looked on our cell phone bills for calls made and there are a lot of short ( 2 minute or less) calls that he made to her and vice versa. However since he said he would not call her there have been no more phone calls that are on the bill.
the phone numbers of text messages made by him and to whom are not shown on our monthly cell phone bill at all.