and because he knows I have an issue with it he chooses not to tell me who he’s talking to or what about.
If he knows you have an issue with it, he should be doing the exact opposite of that. He should be being very open and reassuring. I mean if they are just friends he should be making it really fucking clear there is nothing to worry about.
What he is doing is simply making his life easier for himself because he knows you have an issue with it and its EASIER for him to just not tell you. He can't be bothered, because he doesn't care that it upsets you. These 'friendships' and his ego boosts and easy life are more important to him than your feelings about it.
It is normal for men to have female friends for many reasons. It is not normal for them to segregate them from their partner and keep it all on the hush hush.
He is reasoning it as your problem. Making you feel like you are the unreasonable one. YOU have a problem with it. Its not HIS problem. But he knows full well he is 100% responsible for causing this problem and can sort it out in a second. But he is choosing not to because he enjoys the ego boost of being the 'nice guy'.
And i'll bet he even tells you he helps them because he is 'a nice guy'.
Nice guys help others, yes. But not at the expense of their partners security and feelings. They also have no need to announce they are in fact 'nice guys'.
His wife left him over it. He knows, trust me. He sounds like a typical selfish prick who thinks he can do what he wants, when he wants, with who he wants.
Is it acceptable?
Not how you have described it, no. The unacceptable part is all the behind your back stuff.
Should I accept it and let him in and start to Plan to build our lives together or keep him at arms length because of this issue?
Why should you accept it when its upsetting you? Ask yourself this question. If there was something that you were doing which was making him anxious or upset, would you just think tough shit and carry on doing it or would you try and understand it, address it and come up with a solution?
It makes no difference how unreasonable he thinks or tells you you are being. It matters to YOU. And he doesn't give a shit.
Think of it this way. Lets say he had a total aversion to red nail polish. hated it, made him upset every time you wore it. You might think wtf, thats ridiculous. Would you then purposely continue to wear red nail polish? Or would you think, ok, i think its nuts but I want to be with him and as it really matters to him I'll stop because I care about his feelings and he is important to me.
Its not controlling, its simply expressing something that upsets you that the other person is doing. How they choose to address it speaks volumes about their feelings for you.
And being concerned about his insistence to 'help' all his single female friends he plays white knight to is not an unreasonable thing to be upset about.
I get dating is a pain, but don't let this one in OP. He will hurt you. He is hurting you already, thats why you are here asking this question.
Personally i'd leave him to it and start focusing on finding someone who actually makes you feel safe and doesn't purposely do things to make you insecure while throwing it onto your shoulders as a 'you' problem.