It is possible for a serial cheater to become a monogamist, but it would likely require a significant amount of self-reflection, therapy, and effort to change their behavior.
Serial cheating often stems from underlying issues such as a fear of intimacy, a lack of impulse control, or a desire for attention or validation. These issues may need to be addressed before the individual can successfully commit to a monogamous relationship.
Therapy can be helpful for individuals who want to change their behavior and address the root causes of their infidelity. In therapy, they can work on developing healthier coping mechanisms, building stronger communication skills, and improving their ability to manage their impulses and desires.
However, it is important to note that changing ingrained behavior patterns is not easy and may take time. It is ultimately up to the individual to take responsibility for their behavior and actively work to change it. It is also up to their partner to decide whether or not they want to continue the relationship and support them in their journey towards becoming a monogamist.