Oh dear, I suspect you're already halfway towards having an affair if you're coming up with counter arguments to the reasons why you shouldn't go further with this.
I'm not judging how you feel. Falling in love is a wonderful feeling and can be all-consuming. It's very, very hard to deny yourself that, especially if your own marriage is far below satisfactory.
However, in my case I hung on to my sense of self. I knew that once the headiness had faded (which it always does, even in cases of the 'real thing'), I would be left to confront my own behaviour and motives, and liking the person I saw in the mirror every day was more important to me than hot sex or butterflies. I would find losing the object of my affections much less painful than losing my self-respect and integrity. Plus I'd be damned if I'd let any man have such an effect on me that I would behave so completely out of character.
Ultimately, whether you do or don't, it's a choice. I'm not saying it's an easy one, but it is a choice. You can't excuse it with statements like "I fell in love, I couldn't help it, it just happened" because they are all excuses and something you have a lot more power over than you think - you just have to choose to exercise it.
If your marriage is that dull, call it a day or work on improving it. Sometimes the potential for an affair can be a good thing because it encourages us to realise that we only have one life and it's too short to waste in a half-dead marriage. But the solution is leaving or improving, not having an affair.