He isn't going to stop, unless he wants to.
Chances are, he isn't anytime soon..perhaps this will remain a constant for the remainder of his life.
Both are being disrespectful.
Please learn how to respect yourself and learn how to love yourself...perhaps therapy would be beneficial for you.
You have probably known about this early on and have remained...even if you just became aware, you are choosing to remain ..still hoping he will become your ideal partner.
It's not weird for him to vent to his alleged friend or someone he feels comfortable with about anything (you're on here venting about him).. it's not inappropriate to communicate with anyone daily...
As long as there is balance, respect for your partner and relationship. It's not appropriate that he's acting as if he were single, disrespecting and neglecting you.
You are aware of his behaviors, and you are aware that he prefers to communicate, devote a lot of time, energy, and attention towards her and their dynamic.
There isn't anything to work out. He prefers her over you.
Don't allow yourself to remain a doormat.