Trauma from past relationship

I need advice. I was married to a gaslighter for 20 years. Years of emotional, physical, and mental abuse my entire life has screwed my up. I’m in an amazing relationship now. We actually started as FWB because both of us were scared of relationships, but we became best friends and then realized when we tried to stop the fwb we actually fell in love. My problem is, things are great. He tells me he loves and misses me. He text daily. We talk all the time. We are together as much as we can be. (I’m a single mom with three teenage kids at home/different schedules etc..) but I’m unconsciously driving myself crazy thinking he’s going to leave me. Whenever i see him active in fb I’m like who’s he messaging? Does he want someone younger or more attractive? Is he flirting with women at work. He knows about my fears. We have talked about it several times. He’s even said he hopes to be the one to break me from the fear and cycle I’m always in. He’s always the one who mentions getting married in the future. Building a house together. So why can’t I believe him. I’m driving myself crazy and can’t seem to just enjoy our time together. Live in the moment. Trust him. I need advice please. I don’t want to ruin our relationship because of my fear and trust issues. Please help.