Is he in denial she wants more?

my boyfriend and I have been dating for the last 4 months. About 3 months ago he went out with his best friend who happens to be a girl he dated years ago. They called me that night on their way to a bar. She gave me red flags by throwing in my face I hadn't met his family yet, and saying she laid for dinner one of the reasons they broke up. I told him how I felt and he brought up how she asked him to stay the night. I thought then he would distance himself from her.

This week was her birthday and he posted a few pictures of them on Facebook. I went back through and saw just how many pictures of them together there are versus very few of us. He brought up how I didn't trust him, she had mental health issues and not many friends.

While he's pretty good with me in private and out in public even my friends are asking what is going on. I feel that she wants him and either hes truly blind to whats going on or really doesn't know how a committed relationship works.

My heart is torn as I shouldn't have to worry about another women this way. I do care about him but what's going on isn't healthy for us.