I need help on how to deal with my insecurties and his ex's?

[confused]

Hello everyone!

I have been with my boyfriend for 6 years and are planning on getting married and only now have I become insecure about my boyfriend’s past!

I only found out now that he dated a girl before us for about a month and had been checking her Facebook lately. I know that he had dated another girl for about 1 year before us, didn’t know about this one. BTW He is my first.

I feel VERY insecure. I have no idea why! He never talks to her. They have no contact that I know of. I feel like she is pretty, she is in the same professional field as him (so they can meet up in the future), she looks like a very nice person.

I feel dumb! I need help on how to get over this. I have talked to him about this and he says he loves me very much and would NEVER go back to her ever. But why would he look at her Facebook a number of times if he doesn’t care about her? Does he secretly still have feeling for her but is scared to take it forward? I asked him this and he called me crazy lol And I feel crazy. How do I make this go away? Ugh I feel like a monster

I am a mess! help before I ruin our relationship please!