Am I over reacting? Bf closest friends are women

Been in a relationship with my boyfriend for over 6 years and I thought things were going good but now I am not so sure. When we met I found out his 2 closest friends, best friends I'd say, are women. I had never been in this position but it helped that he told me they are a couple, which I believe they are, although if they are they are in the closet but we are all middle age so that doesn't surprise me really.
He gets 5 weeks of vacation a year and any left over from the previous year and I had pretty much accepted that most of that time was spent with 2 other girls. He has known them for years from work and after he got divorced they got closer and he is like a part of their family. I admit I had a few jealous twinges when he would go off on a fishing trip or hunting trip for 10 days with 2 other girls, which they do both every year now, but I always got over it and I figured it was somewhat normal to have a little jealousy and considering what I consider most of his quality free time is spent with them I thought after 6 years I was doing good! It's not that we don't do a few things together and I have done a few things with the group as I call them.

Here is the little thing that changed everything for me. I found out about 3 months ago that he is keeping things that have to do with them a secret. He does things with them and for them and he just never mentions it and it makes me wonder why? I found out because he had a day hunting trip planned with one of the girls brothers, who is also one of the group, which I knew about and heard all about when he got back. He likes to talk and tell stories of his adventures only he left one detail out. We are all friends on FB and I saw a post from the brother thanking both his sister and my bf for the outing. I know it's just a little detail that is why I wonder why he left it out? When I asked him he said because he wasn't sure how I would react? Well that confused me because he knew I had jealousy issues on a small level with them and I have reacted the same way for years. Actually as I started feeling more a part of the group my jealousy started fading a little so his reason made no sense to me. His keeping it from me only made me suspicious.

Let me explain my jealousy, I am 99% sure they are a couple and I am almost positive he is not cheating with them, for clarification I will call them g1 for girl 1 and g2. I had heard all of their adventure stories before I even met the group, like I said my bf likes to talk. As we were getting to know each other a conversation led to me asking if they had seen him naked and he said kind of, they saw him in his under shorts. So I asked if he had seen them naked and he said in their tee shirts and panties. So I ask how this came about.
This all happened about 5 years before we met, he says that g2 was still married and going through a divorce and he was newly divorced and they were hanging out and g2 wanted to get away from her soon to be ex so they went out to the camper to watch a movie. The only place to lounge and watch is the bed and they might fall asleep so they got into their "sleeping clothes" he called them to watched a movie, like that is what everyone does. He said there was never anything sexual, no kissing or touching went on and I asked if he wanted something to happen and he said no. Although I couldn't wrap my head around 3 middle age people who are only friends stripping down to their skivvies to watch a movie, I let it go.
After that I started getting a bad gut feeling sometimes and I might have gotten a little more jealous but I didn't hide it from him. After a couple years when we had another little bump in our relationship I brought it up and how his reason, to me, was absurd and he admitted that at the time he was hoping to get some, and that it was his idea to strip down, but that it never happened. And I believed that more then what he said first.
But after I find out that he is keeping things from me I have begun to question everything, Since I found out about the skivvy incident I have been on 4 or 5 outings with members of the group and I thought after 6 years I was finally getting a leg in the tight knit group but now I don't feel like part of the group at all and it really hurt my feeling that he would keep his contact with those 2 girls from me. I was never a crazy jealous person, just a little somber when he would leave, maybe a little quiet when he told me all about his fun time when he got back, plus I might have made a few sarcastic comments like calling them him wives but we have never had a arguing fighting type relationship.
He just says he loves me and has never cheated on me and then acts like I never said anything. I told him it hurt my feelings and that now I was suspicious but he never has much to say. I think he just hopes it will get better, and because of my age I think he blames it on hormones, who knows maybe some of it is!
There are a few more small things that bother me that I had let go and thought of now that I feel hurt and confused but my main problem is that he kept things from me about people he knew I had jealousy issues with and I feel like a fool, they know more about what he is doing then I do a lot of the time but my question is am I over reacting? I don't want to end something that is good but I can't spend our whole relationship wondering what he is keeping from me.
Everything seems so messed up and if it don't change I think my jealousy will get worse. Please any truthful opinions appreciated. thanks for reading all this, hope it makes sense.