<human>: Could you distill the essence of the text into 1-3 sentences?

Throwaway because I am embarrassed at myself for feeling this way. 

My boyfriend Ryan and I have been together for 8 months. He's a great guy. We both had said that we were each others' best relationship. 

Ryan spends a lot of time on Facebook because he works from home on his computer. 

Every once in a while when I'm browsing Facebook, a post will come up saying "Ryan has liked Brittney's photo." All her pictures are public so whenever this happens it shows up in my newsfeed. They are always her selfies and are never recent. They are usually at least a few weeks old. She is single and goes to the same college as me but I don't know her. It should be noted that she's very beautiful.

Whenever Ryan and I go more than a day without seeing each other he will go through my Facebook and like old pictures of me. I always thought it was very sweet until I saw him doing this with her.

I feel like he would leave me if she expressed the same mutual interest in him. I know how insecure I sound which is why I'd like some advice for how to deal with these insecurities.
<bot>: What can I do to not feel this hostility towards my BF whenever I see that he liked one of her old photos again?