Oh man, I can totally empathise with this situation having been there myself. Big time.
For me the main worry was the fact that I would get excited to see "mr hottie" at work and, knowing myself from previous relationships, this isn't something I do when I'm fully satisfied in a relationship.
I know it's different for everyone but, for me, when I'm head-over-heels for my partner, I go blind to anyone else being remotely attractive in a sexual way. I am very much an "eyes only for you" kinda gal when I'm happy, so the fact I was (still) noticing "mr hottie" meant, for me, that something wasn't right in my relationship.
Secondly, and more importantly in my opinion, I would get more excited to see mr hottie at work than I would to see my OH.
And thirdly, I was stuggling to get mr hottie out of my mind when I wasn't at work. #AlarmBells
For me, it's the hat trick which meant for me, something had to change.
I think in your situation, as long as the new guy at work is:
a) just something nice to look at (like an out-of-your-budget dress in a window - you can still look!)
b) you have stronger feelings / intimate connection with your partner
and c) you're not fantasising about the guy at work instead of your partner / your attraction to the guy at work isn't having a negative impact on your relationship with yourself or your OH...
... then you have nothing to worry about.
Do remember that a huge part of attraction is the "mystery" and right now, he is the new guy. There's a good chance your attraction will wear off as you get to know the guy better, and realise his "flaws". I know that sounds mean, but it's true.
If you get to know him better and your attraction grows or any of the above changes, then there may need to be an honest open conversation at some point.
Please also remember that ALL of these feelings are completely natural, normal and part of human nature. In fact, many sexologists believe humans are not meant to be monogamous at all, so even though these feelings may not be convenient right now, they are totally natural and just part of what makes you, you! And the only reason you're feeling "bad" for them is because marriage comes with certain rules, commitments and promises which these feelings, if left unchecked or uncontrolled, could lead to one of those rules being broken.
If we lived in another plane of existence, a society which had fewer expectations and rules for how love is expressed, chances are that the above would come with a lot less guilt.
I'm not sure how helpful that is... I just relate to this situation so much so thought I'd share my 2 cents!