IMO that you feel being with her would "make me happy, bring me new happiness and excitement" tells you what you feel you are missing in your life now.

I think the phrase 'hitting it off' is really telling - that is what we do in the beginning stage of any relationship. I have no doubt you could 'hit it off' with a variety of different people if you and they wished- that is the easy part. The less straightforward part is building a life together, raising children, being a team, and nurturing the love you have. If it were easy these forums would be empty.

New attraction is exciting and giddy, it makes us feel alive - the reason for this is the hormones we are producing, this infatuated state only lasts a few years on average, if it lasted longer we'd wear ourselves out. Personally I think you need to think very carefully about the whole situation, focussing less on this current infatuation and more and what you need in your life/marriage to make yourself feel happiness and excitement again.

If you and your wife do decide your marriage is not working out I'd strongly advise talking it over with her/coming to the decision whether to continue or not before you approach any other woman. Ask yourself what you would expect of your wife, how would you feel if you knew she was approaching another man (acting on it is a big difference to being attracted to someone)? It's a good rule of thumb to how you should behave yourself.