You are in danger all right. The danger lies not in the fact that you are attracted to another man (it is common to be attracted to many people); the real danger lies in the fact that you feel the need to act on your desires.
I think part of your problem stems from the fact that since you have been married you have not found yourself attracted to another man. Because you haven't been tempted until now, you haven't been forced to sit on your desires (no pun intended). Until you have fully analyzed what is happening to you, you should not engage in any action whatsoever.
Let's begin our analysis by studying why are you in such a hurry to act. Do you have a problem controlling your impulses? By this I mean do you tend to act out whatever feeling comes up?
For example, if you feel angry, do you kick, punch, slam doors, throw things or say words that land like blows to the head; or do you control your urge to act, sit back and think about what you want to say and/or do before you act?
If you choose the first option (react before thinking), you are an impulsive person who needs to learn to separate feeling from action. This skill involves training yourself to tolerate the frustration that comes from not gratifying your urges, especially urges that aren't in your best interest. The skill of resisting gratification and tolerating frustration is hard for many people to learn, but it is a vital skill to acquire if one hopes you to succeed in life, work, and relationships.
Next, figure out why this man has your head so spinned around. You say that you love your husband and that your marriage is good. Are you sure? Usually a person doesn't fall into another's arms when a marriage is working fine. Is something missing in the marriage that you haven't wanted to admit to yourself? Cheating is often an act of aggression against one's spouse. Are you angry at your husband and not aware of it? Is your husband meeting your needs in important areas? Do you see this other man as possessing traits that your husband lacks? Do you imagine that this other man can meet needs that your husband doesn't?
When you figure out the answer to these questions, you will have a better idea of what needs mending in the marriage. I don't think that you would be so vulnerable to acting on your attraction if all was so fine on the marital front. You also need to examine if something is missing inside yourself. You mentioned, in passing, that you have never been with anyone besides your husband. Do you know how you feel about this? Are you experiencing a mid-life crisis in which you are feeling the urge to experience what you have missed before it's too late?
If this is so, perhaps you can find a way of fulfilling these unmet needs within the marriage rather than living out fantasies that will risk the marriage. You also need to seriously consider the impact that an affair will have on your marriage. Are you prepared to break the marriage up?
If not, then you shouldn't be cheating on your husband. If you are willing to end the marriage, then having an affair is a good way to start that ball rolling. If the marriage is lacking, the safest course of action is to address the problem areas directly, rather than cheat.
Cheating may provide gratification in the short-run, fill voids that aren't being met in the marriage, or even satisfy your own wish to widen your experience. However, you need to seriously consider what risks are involved in giving in to your urges.
Also keep in mnind that cheating will damage your self-esteem. No one can feel good about herself when she cheats on a mate. Are you willing to bear all these risks?
If your answer is no, then don't act on your urges. Once you have fully evaluated this temptation, you will be more able to make a clear and rational choice. Your actions (if any) need to be the result of a cool-headed decision that is based on a complete understanding of all the dynamics involved.
Until you are clear, do nothing.