A.B.
You wrote: How do I get my point across to him?
I have learned that the only person whose behavior you can control is your own. With others, you can teach them how to treat you and pray that they will have godly examples and mentors in their lives. And, with children, you can raise them by teaching them what is right and what is wrong and be that mentor and example to them. You can teach them about choices and how those choices have longlasting effects. They cannot choose the consequence, but they can choose the action. Nothing more.
You wrote that to your knowledge, "he has not had [the girlfriend] around [your kids] again because the doors to the 'great beyond' opened up for him after that incident." So, is this still a problem? Maybe it is, maybe not.
This is what I would do. I'd call to ask when he'd like to see them. Then, I'd ask if he had a minute to go over how we're going to handle raising them apart. If you want him to continue his father role to your children, what are the rules? For both of you? If he thinks it's ok to bring other women around them, ask him why? Listen to his answer. (Even if it sounds stupid to you, don't judge it.) Then, I'd ask if he thought it was cool for me to bring other men around them. I'd do that just because it would teach me how he thinks about raising children. Not because that's my intent. Listen. (Even if it sounds stupid to you, don't judge it.) Then, I'd ask him, calmly, "What do you think our children will think when they see different people in either of our lives? Is this the kind of relationship either of us should model for our children? Do you think our children should accept that as the standard for their relationships? And, if they get attached to a future 'friend' and it ends, how do you think the children will feel?" Do not yell at him or curse him out. That's for your benefit. Thank him for his honesty and ask him some other things, like what about parties around the kids? What movies? Music? Discipline? Religion? Extended family members? If you two do not agree on any of these subjects, then you have some thinking to do about how much time you want your children to spend with him. His answers will teach you more about who he is, how he thinks as a man, how he thinks as a father.
Then, I'd spend some time teaching my children what is right and what is wrong. They are so young, but they can understand something as simple as "You know that Mommy and Daddy are not together anymore but we both love you. People make mistakes in life, but we can forgive each other and keep living. We get hurt when people do things without thinking about how it makes us feel. As human beings, we should do our best to choose right over wrong. I am sad, too, but I do not hate Daddy. I don't want you to hate him either. He still might do things that are not right. But, we can forgive him and pray that he learns how to make good choices." Then, teach them that Daddy will have to want to change, but if he doesn't we can still love him. We do not have to do what he does and maybe one day he'll make better choices. Do not to hate him, judge him or make him feel bad." I'd teach them about the reality of life, that people make choices for selfish reasons or because they have not been taught or had an example of what to do, and sometimes they do not stop to think about how other people will feel. Our goal as human beings should be to try to live above our selfish wants and do our best. Yes, we make mistakes because we're not perfect. But, we should try our best to overcome those things and have peace in our hearts and minds.
You have a good attitude about your own dating habits. If they see Dad making mistakes but Mom's conducting herself in a way that doesn't bring more drama, they might make the choices that will bring peace as adults for themselves. Whatever you want for your children, you have to model it first so that they know it's even possible to achieve. Do not judge how Dad handles his other children. He has to deal with that.
