Feeling lost, need advice

Me and my bf have been together for 8 years now. We've been through so much stuff together and even through the worst we have managed to stay together. Lately I've been thinking about all the worse parts of our relationship and feel as if we never really worked things out but just swept it under the rug and pretended things were ok. I have a feeling in my gut that he's hiding something but whenever I ask him if things are ok with us or if he's going through something he says he's fine. His attitude is different, we don't spend time with each other on my days off, he snaps over every little thing and I just don't know what to do. Like I feel as if he is hiding something but I don't want to snoop to find out because I know he won't be honest about it from past experience. And if he is hiding something I know I need to end things and walk away for good because I've given way to many chances in the past. My biggest fear about leaving is our kids and starting over with no help. Maybe that's why I've stayed through everything before. Sorry so long, just needing to let it off my chest and get some advice.