Dear MissKnight15,
Irrespective of what the definition of an abusive relationship is, or whether you are in an abusive relationship....what a crappy marriage it is to be in. There's cheating, death threats, abuse, belittling. How can anyone sleep next to a spouse peacefully who threatened to kill them. What do you think will happen to someone's health (physical and mental) if they have to sleep with one eye open?
If you are staying for the kids, what do you think your sons and daughters will learn about love and relationship from this? If you are unhappy in this relationship, you are probably passing on mental health problems to your kids (like cptsd, depression, codependency, etc). Everything you've described sounds traumatic and exhausting.
As someone who came from a broken home said "Better come from a broken home than be in a broken home".
To answer your question if you are being abused, I think you already know the answer - yes.