Marital issues, advice please.

Weve been married for 6 years, together for 10. First couple years things were great, or so i thought. Issues started about 3 years ago, the first time he brought up divorce. Claiming he's been unhappy the whole time and we're so different. He's since brought up divorce 3 or 4 times and has talked about moving out too. Ive never brought up divorce. I have the mind set that id rather work on our problems than lose my husband and raise my son in a broken home. My husband seems to be the run away type. I've been able to sit down and talk him out of it but its tiring and quite frankly changed the way i look at my relationship. I feel very insecure in my marriage. I feel like even if he's happy in the moment, I'm just waiting for the other shoe to drop and for him to want to leave. It hurts. Anytime i try to convey my feelings, he gets defensive and will say he can't do anything right and get mad instead. So i choose to just silently deal with most things. When things are good, he's happy and loving and a good dad but when things aren't, there's extreme negativity and depression. He has some pretty bad mood swings when things don't go his way. For ex, he had the last 2 weeks off of work and had some things planned. Things that didn't go according to plan: 1) didn't get the xmas bonus he was relying on and already spent $ assuming he'd get one 2) it wasn't cold enough for snowboarding 3) my son and i are both sick so didn't do anything for nye. So i get being disappointed but im talking locks himself in our bedroom all day while I'm left to tend to our son and the house while sick. Silent treatment to me and our son. It ruins the vibe of the house and everyone notices. And this is what happens everytime and ends up turning into a downward spiral that gets worse and sometimes will end up in divorce talk from him. I have asked him to do therapy whether it be just him or both of us. He refused. I truly think he has some untreated anxiety/depression issues but won't get help. I'm tired of walking on eggshells and never knowing what mood he might be in. Thank for reading if you've made it this far. What do i do? Any advice? Anyone been in a similar situation?