Leaving an abusive relationship is never easy. There are lots of reasons to stay.
Your spouse is probably not always difficult and abusive. The nice periods give you hope that things will improve.
Your spouse was probably very charming at the outset of the relationship, which is why you were attracted to him. Your spouse continues to be charming to others, so you know that charming person still exists.
Your spouse makes you feel that the abusive behavior is in reaction to your shortcomings.
Sometimes, the abusive was incremental. Overtime, you began to accept it as normal.
You may be financially dependent on him.
You have children together and you have the dream of having a healthy, intact family.
You may have been raised in an abusive home and see the high conflict as normal.
There are more reasons. However, when you realize that the conflict level is abusive and others tell you they fear for your safety, it's time to take action. Start with seeing a counselor for yourself, preferably someone who has experience with spousal abuse. The counselor can help you access whether the conflict between your spouse and you is within normal ranges or whether it is abusive. If it is, ask for a safety plan from the counselor. Most domestic violence shelters make safety plans available. Contact a shelter, if you do not have the resources to see a counselor or want more education.
It is probably not possible to get out the relationship by being nice. Your abusive spouse has a need to control and hurt. This person is not going to let you go nicely. You are going to need a lawyer to help you who has experience with domestic violence. You can make it easier on the lawyer if you are candid about what has been happening in your home. Make a journal, with dates and time and a description of the incidents. Domestic violence does not have to be recent physical abuse. It can be barring you from leaving the home, or going to work, or keeping you up at night when you should be sleeping or being verbally abusive. Tell your story and let the lawyer advise you on the best course.
Leaving is hard to do. It means accepting that your marriage is not working. If you have children, it means critically assessing whether your children are safe with the other parent. It means giving up the dream of your family's future.
Professionals can help you gauge whether ending the marriage is really necessary and the best way of doing this. Especially if your children are witnessing the violence or high conflict between you or if they are the objects of the violence, you have a responsibility to act to protect their safety.