The short answer to your question is “no.” You probably shouldn’t give him more chances. You two are in your 40s, so this is probably a long-established pattern of behavior for him. Although you have been together for a year and a half, your boyfriend isn’t willing to become a faithful partner. He has lied to you and refuses to let you meet his so-called “friends.” I suspect that he is going through the motions at the class in order to keep you in his stable of relationships. He has no intention of really changing.
One of my teachers used to say, “Two relationships are fewer than one.” What he meant is that by having many relationships, a person doesn’t have to take the emotional risk that is involved by becoming a loving and exclusive partner. I don’t have the information needed to help you understand why your boyfriend needs to protect himself this way. I do know that when someone has a long history of his kind of behavior it takes a great deal of motivation and often intense therapy to change it.
I’m sure there is something sweet about him since you (and the other women in his life) do care for him. But I think you are setting yourself up for more hurt if you try to make a marriage with this man.
I wish you well.