Just "No Filter" or Cause for Concern?

Hi there. So, a little background. My husband is 32 and I'm 34 and we have three beautiful little boys together, ages 5 and a half and under. We have been married for almost 7 years (this December). I believe he has ADHD, as he was diagnosed and medicated (Ritalin) as a child and still displays many of the symptoms to this day (he's not on meds now and hasn't been for years). His bio father also has ADHD. He is adopted and has wonderful adoptive parents. 

Here's what's bothering me: When he gets upset, he has no filter and doesn't control his words. For example, when we're all riding in the van and he gets upset, perhaps if I take away his cell phone and prevent him from texting while driving, he'll make this comment: "I'll crash this van and kill us all." Or when he's depressed about work deals not going right, he'll say, "I should just throw myself under a bus" or "I just want to die". The most recent (and most upsetting) thing he said was the other night when we were about to go to bed and I was telling a story and he wanted me to be quiet. He said, "I'll smother you with a pillow." Really?!!! I didn't say or do anything that would justify such a terrible statement!! Since then, he's apologized, we talked it out, and things are supposedly ok between us, but I still feel very unsettled and upset. I told him he needs to go to counseling with me and I found a therapist that our pastor recommends, but he's very reluctant to go because he doesn't think there are any problems. I told him that he cannot make any of those comments ever again because it's not healthy for our kids to hear those statements (thankfully they were all asleep when he made the "pillow" comment). I still feel horrified. I serve this man all his meals, stay at home to take care of the kids, and things had been going so well with us prior to this. I always dismissed his inappropriate comments as just having "no filter" because of the undiagnosed ADHD, but how do I know if I should be more concerned? He's never hurt me or the kids. The most he's ever done is slam his fist down on the kitchen table. Am I overreacting? Does this sound like typical ADHD or something more severe?