I need relationship advice :/

I've been dating my SO for quite some time now, but I still have issues trusting him. But I feel like it's not because of him, it's because of other women... I know I have my insecurities and I'm trying to get over them. I'm very possessive of my SO, to the point where I've unintentionally ruined 2 of his friendships just because of me being worried about them trying to take him from me. I catch myself constantly checking if he's active, or when he was last active, etc on Facebook. My emotions are controlling me more than I can control them. I am always skeptical with no real reason to be...  I don't want to stay like this but I just need some advice and reassuring words because I really do love this man and our family together. I don't want my personal issues to sabotage our relationship. Thank you in advance, and if there's criticism, please make it constructive and not judgey or rude... I genuinely want to fix myself.