should I end things?.....but I'm madly in love with him

Long story short, my boyfriend has this Facebook friend who always like his statuses and hearts his photos. She goes to the same college as us and in the same grade and major as me. Now me and him aren't friends on Facebook because he refuses to add me claiming "social media ruins relationships"  everytine I see she has liked something my stomach gets a deep weird feeling. I feel like he flirts with her. He hearts her photos as well. I know this cause I snooped on her page. When I asked about her he told me that was his "homegirl". Then all of a sudden the "add friend" button isn't there anymore. I came to the conclusion that I don't trust him. The more I think about him cheating on me with her I become sad and less uninterested in the relationship. I try to distant my mind from it but I can't. I really don't know what to do. I prayed for God to reveal to me if he is cheating but idk if this is it. Please help me.