You have a difficult choice. Different cultures solve this problem in different ways. In France, you would keep your old stable relation and still enjoy a new infatuation while it lasts.
In Sweden, the common solution is sequential polygamy. People switch partners, but have only one at a time.
You have to decide what is most important in your life, peace or passion. The risk is that you will have neither, when the new passion ends. The choice must be yours, because you have to take the consequences of your decision.
Love and infatuation is a trick of nature to produce more babies. But after a year, only a small percentage are still in love. It is not fair to compare a man you have just fallen in love with, with a man, who you are not any more in love with. You see the new man in a rozy haze, while you see the old partner in a more realistic way.