Is it possible for a cheater to change?

It's possible for anyone to change.

No idea whatsoever if that's the case here.

People are very good at claiming to change, and they do, for about five minutes.

Unless your married it does not count. In fact it should be in the actual agreement. Beyond that it is just dating and nobody holds any obligation to the next person. At anytime her/him could change opinion in mind.

Anything (in this arena) is possible. There's decades worth of unfaithful partners who have turned their cheating ways around. Depicted in fiction and memoirs and lived peacefully and lovingly with their present life-long partners for decades after their assorted affair(s).

No one here is going to be able to predict the future behavior of the alleged partner you are referring to.

Cut your losses. Chalk it up as bad investment. In a lifetime of relationships, you’ll learn to make much better investments

Possible. Not likely, particularly if the driving issue for the cheating isn't remedied.