It is absolutely clear that the environment in which you live is very heavy. Keep in mind that a separate apartment in a shared house was not a good decision. It seemed to be perfectly reasonable, but did not take into account your emotional state. It does not matter why you separate yourself with your husband, the fact is that you have not yet been remodeled emotionally. Maybe after the separation, you still expect them to come together again, especially because they live in a common house. It is possible that you will not even realize that. It may also be a reason to decide to stay with your ex-husband in a common house. You felt good until you created a new family. It is not a coincidence. Since then, as you say, everything is wrong.
Your reaction and your behavior tells you that you are still very emotional to your ex-husband. It hurts you because you are seeing that he manages his life. With another couple, they created a relationship that you may never have had, or that's just the beginning. You may be accused and inferior to your feelings. After three years of separation, he experiences a serious loss of life that can not be taken and overcome. Ask yourself why you do not create a new life in your own way, just like your ex-husband. Try to figure out what the lame prevents you. You may be afraid of changes in life, you have a bad self image and a low self esteem. In any case, look around yourself and you will notice that there are many women separated from you and who have organized a new life, with or without a new partner, as it suits them. If others can do this, you can do so too. You just have to believe it. It's time to leave what you have left in the past, because nothing can be repaired or altered backwards. Only you can forgive yourself and others and keep going, towards new challenges. You have a child in the years you still need a lot. You need a mother to be calm and to feel the joy of life. Make sure this feeling is once again established. Dedicate to the activities that you like, do not forget to get in touch with nature, which is a balm for soul disease. Create yourself and trust and you will succeed. Even the housing problem does not seem insoluble. If there is no other option, you have a flat that you can rent and hire another. Of course, you have to leave the house. Only then will you be different from your husband and give you the opportunity to emerge emotionally completely. Whenever you are in touch with him, also indirect, everything that is bad and good has experienced you during all the years of your life.