Hi and welcome
Impossible for anyone to judge if you are in the right or wrong when we know virtually no details. Anyway this forum really isn't about judging it's about supporting, giving opinions based on experience and sharing (that's my take on it anyway).
Can you give us some more details like:-
Have you shared this with your husband?
Is this new man in a relationship and if so does his SO know?
Have you discussed where you would like to take this with any party?
Why has there been no intimacy in your marriage for so long?
These are the places I would start.