Unless there is more to this than you presented, you’re quite right. Your girlfriend’s reaction to your ex could well end your relationship. When adults begin a new relationship, they come with a past. Your divorce sounds much healthier than your girlfriend’s. You and your ex understand that you divorced each other but neither of you divorced your daughter. You are doing your best to be supportive co-parents even though you couldn’t find a way to continue to be married. This is healthy for everyone. Your daughter doesn’t feel like she is caught in the middle between two embattled parents. You both allow her to love and be loved by the other. You and your ex maintain a healthy respect for each other and have each moved on to finding new love.
It’s sad to me that your girlfriend doesn’t understand that all this speaks so well of your character. There is no reason for her to be jealous. You’ve moved on. There is no need for her to react as she does when you talk about your daughter’s relationship to her other family. It’s no threat to her and your daughter needs to know that you support her relationship with her mother and stepdad. Ideally, your girlfriend would find a way to be friendly with your ex and supportive of your role as a co-parent. If the two of you move to the next level or marry, she’ll also be co-parenting your daughter. She needs to be able to have reasonable and respectful conversations with your ex if you’re not available and decisions have to be made regarding your daughter or if your daughter needs something left at her other home.
Ideally, at some point you’ll be doing the same with her sons’ father. Your girlfriend can’t erase her past either. Whether or not he lived up to his responsibilities, he is still their father and the boys need to be able to speak about him and perhaps visit him if it is safe for them to do so. Even if he is an abusive parent, supervised visits may need to happen at some point so the boys will have a realistic understanding of who their father is.
You say you went to counseling. I hope the counselor was able to be sympathetic to your girlfriend’s desire to have you all to herself but was also able to help her understand that it’s not a realistic or even healthy option at this point. If you feel the counselor didn’t do that, perhaps you didn’t provide enough information about how extreme her reaction is and how potentially harmful it is to your daughter. If that is the case, I hope you’ll make another appointment to present that information. We therapists only have the material we’re given to work with. I do hope you found a counselor who is experienced in family therapy. If not, please consider trying again with a new one.
Whether or not counseling is successful, you and your girlfriend need to have a serious talk. Her reaction to your relationship with your ex is a deal-breaker. If she absolutely can’t tolerate it, you should wish each other well and move on.
I do wish you both well.