How many of you follow your instincts about your SO?

I have always gone with my gut when it comes to relationships and they were almost always right, almost. But this time I am completely torn. I feel like there is a problem in my marriage. I don't know exactly what could or would be wrong. Most of the time we r here alone but I have this this with him masterbating and I have asked him not to several times and a couple months ago we got into this big fight because I wanted to have sex one night and he said no and I found out a couple days later he masterbated that night so since then I've been kind of worried but it got worse when his ex came over for the night. I was with them all night and nothing happened but I just got this feeling that night and it won't go away. I have my hubby's passwords for everything and he doesn't seem to care. I just feel like I'm going crazy. Any advice?!