How do I fix a relationship when we’re both unhappy? We both used to be very happy.
I'm so sorry you are having communication issues in your marriage. It is a very common problem in relationships and can definitely lead to strain and distance. Repairing communication can be a long painful process and I recommend you start couple's therapy so that a therapist can help you mediate and learn to communicate more effectively but I have outlined some steps you can do on your own below.
The best option is to communicate to him by calmly explaining that you feel he is becoming distant from you. Be sure to do this at a time when you are not already upset and make an effort not to become defensive. If you are already fighting, anger and stress will make it difficult for you to stay calm and rational and you are both likely to say hurtful things. Wait until you are both in a calm mindset and spend some time having a conversation, not an argument. If the conversation begins to turn heated, calmly suggest that you take a break and return to it at a later time, just be sure that you do return to it and don't let the conversation disappear again.
Take time to listen to his answer and reflect back so he knows you hear him. For example, if he says "I just like having someone to talk to" you can respond with "I understand you want to feel heard and I want to be the person who listens to you, please let me try." It is also important to tell him how you feel, make sure to share how much it hurts you that he speaks to her so much. It is okay to think through how you want to say this to him and writing it down can be a very productive way to explain your thoughts without letting your emotions drive you. I often suggest writing an unedited letter to someone to purge all the emotions, no checking grammar or spelling, just let it flow. Then burn or shred that letter and start a new one where you spend more time thinking about what really needs to be said and focusing on statements that explain how you feel and make specific requests like "I feel extremely betrayed when you turn to her for conversation and companionship, please try to call me first in the future so I can be that person for you." When the letter is done, find a time to sit down with your husband and read it to him, start by asking him not to interrupt and explaining that he will have an opportunity to respond when you are done. Take your time, stop and take deep breaths if you find yourself getting upset, and listen to his response when you are done. If reading out loud sounds like too much, you may give him the letter to read and ask him to write you one in return, sometimes this is an easier way to start an emotionally charged conversation.
If after all these efforts, he is still not taking your concerns seriously, I strongly recommend getting into therapy with him so that you can both have a chance to work on communication and reconnect with each other. I wish you the best and hope you are able to heal your marriage soon. Take care!