<human>: Can you succinctly summarize the text in 1-3 sentences?

My BF [20M] and I [22F] have been together 7 months. Previous to our relationship, we were best friends. When we first met in Summer 12' he was dating his now ex [21F]. His ex cheated on him several months later and he broke up with her. Flash forward to this past summer when we realized we were perfect for one another and fell in love.

Here's the thing: I cannot stop thinking about her or their past. I'm jealous of it, and I stalk her on social media. She seems like she was a much cooler person than I am, and she was quite thinner, too. I don't know why I can't stop wondering what her life is like or comparing her to me. I've been trying not to do this because it's toxic, but I can't help it, and I've never been jealous before. 

Does anyone have any suggestions on how to quit this? I don't want my bad habit of checking up on her to be an issue in our relationship.
<bot>: BF broke up with his ex over a yr ago, and I can't stop stalking her online. Jealousy issues.