Husband acting suspiciously

So recently my husband is never home. I mean never. He’s always out and makes excuses for going out. Even my kids have been asking about him and idk what to say. He’s stopped wearing his ring completely (especially when leaving the house) and he says he doesn’t need to tell me where he goes because he’s a “grown man”. I’ve thought about going through his phone but I always back out because what if it’s nothing? He’s been really rude to me also just because I ask him to tend to his own kids and I ask him why he’s been out so much. He gets so mad at this and says I’m overreacting and that he just goes for walks or something. He hasn’t been working either. I’ve been trying to be positive about this situation but I can’t keep this up forever. I don’t know how else to confront him and get a truthful answer out of him. Should I give him an ultimatum? I don’t know how to go about this...