Other girls, ex’s and checking them out

I need some advice.

My boyfriend keeps checking out other girls, his Instagram is full of girls, Saturday he checked out a girl walking by and then tried to play it off that he was looking at a lake, later admitted he did.

He spoke to me then about his ex, who he was with for 3 months and said he was in love with her, when they broke up he went around on dates with anyone and everyone. Saying he didn’t care he would sleep with any girl, and go to any date he could get.

Later that evening, he was on Instagram and was looking at pics of Michelle Keegan, and Jac Jossa, making a joke about Jac, and how he wished she would call him.

I feel quite insecure. I sometimes don’t feel like I’m good enough, and I’m scared to tell him, as I’ve told him before and he has told me that I’m silly for thinking it, that he thinks I’m beautiful etc.

I just really don’t know what to do to help these feelings. I trust him, I just am a bit scared to lose him.