Feeling like I'm not good enough


So the past few times me and my husband has had sex he has gone limp within one to two minutes of us having sex. I'm not sure if it's because he's not attracted to me anymore or if I just don't please him or make him happy anymore. And Sunday he went to go clean the garage and I caught him watching porn when I was just right inside the house if he wanted to do something. I really need help ladies because I feel like I'm looking my husband. I've been down this road before. It starts with porn, then chat lines, then them cheating on you. I've tried different things to try and spice up our marriage but nothing seems to work.