First the abuser is romantic, sweet and all the things you want from them. This is usually the side of an abuser that you first get to know. Most signs of abuse will not be evident until after you decide to invest part of yourself into the abuser.
After awhile the abuser has something that they want or need from you. They will present this request as a demand or instructions. This can be done through tone, a look or by words, but the underlying message is that responding with 'no' will result in consequences. In the early stages of relationship the consequences are mild, like pouting or teasing. It is only in a more defined relationship where the consequences begin to include neglect, bullying or physical harm.
If you are able to say 'no' and stick to it even after enduring the consequences then you are very likely going to find yourself experiencing some form of emotional abuse usually in the form of abandonment. Abandonment will usually look like refusal to attend an event, denial of knowing something important to you or ignoring some form of basic human need. This might be considered healthy boundaries in the mind of a healthy adult, but abandonment includes intended sense of rejection in a way that causes as much pain to the victim as possible. The abuser is driven to control, and they will use emotional pain to get what they perceive as control. Every human on the planet naturally attempts to avoid pain, that is why using emotional pain works so well.
Often victims will submit during the abandonment phase and give the abuser what they want, because being rejected is one of the most painful experiences any human can have. After the abuser is appeased, they return to being sweet and romantic often even apologetic for the things they did to cause pain. However, they will usually blame the victim in a subtle way for causing a situation that 'forced' them to use such measures. Many victims will report that the abuser seems to not remember the pain that was caused by what happened even if they can recall the things they did that 'crossed a line'. Apologies in the honeymoon phase are emotional and intended to deepen the victims ability to trust that the abuser cares about them, but the statements and emotion behind the remorse are not necessarily sincere.
Sadly, this cycle continues for as long as the abuser and the victim remain in relationship. The only part that changes within the basic cycle is the severity of the consequences that come with not responding to the demand of the abuser and the emotional intensity of the honeymoon phase. In time, the victim becomes numb to emotional pain as they are exposed to higher degrees of it, so the abuser raises the level of discomfort to get the same response or 'fix' from the victim. In many ways the abuse cycle looks similar to the cycle of increased levels of need and tolerance commonly seen with continued drug use.
Every time the victim submits to the abusers demand the abuser learns that their actions are acceptable to you so long as they apologize appropriately after they get what they want. The more times the cycle plays itself out, the more severe the consequences become.
The only reason most victims stay in the relationship is the cycle. The promise of meeting the victims needs acts as a type of carrot that the victim constantly works to obtain. The abuser learns how to use the victims needs to get whatever it is the abuser wants. Using emotion and manipulation is a life skill, so abusers are literally experts at using these tools to meet the driving need for control.
While the cycle is simple, breaking the pattern is an emotional journey that is anything but simple.