My new boyfriend stalks his ex on social media?

Anonymous
I've been going out with my new boyfriend for 1-2 months. Well I didn't know he had recently broken up with another girl just before we started talking (about a month before.)

He never told me about her, but I came to find out (she and I have mutual friends) that he never told her about me either and they had messaged eachother about a week ago when we were together. She basically rang him and he texted her back in the middle of the night asking why she called. To make matters worse, I saw his search history and that he's been visiting her instagram almost every day even though they don't follow eachother.

I feel so mad and I HATE her. I asked my boyfriend about it and he assured me he wants me and only me, but I feel he's not telling me the entire truth otherwise why would he keep this from me? To make matters worse, this girl is much prettier than me. What should I do?
My new boyfriend stalks his ex on social media?
2 Opinion