My Sales Girl Is About To Crash My Relationship

Hello nairalanders!
I seek your opinion concerning this situation I find myself in.

I have been in a relationship with my fiancée for 3 yrs already to which she is pregnant for me at the moment! Though we have been together enjoying our relationship until recently I employed a new sales representative which is getting me confused.

Since the day I employed my sales girl, she had been handling my business perfectly even while I wasn’t around, she always defends me well, though I pay her well for this, but she had been managing the business like hers and she makes good return daily, besides she is also a good girl in management.

The relationship I have with my fiancée is getting to marriage soon but I feel recently am making a bad choice even though she is pregnant for me.

Recently, my sales girl profess love to me by telling me she really loves me and she has falling in love already, this makes her get pained seeing me and my fiancée together.
I had to explain to her that, I am the kind of person that is very loyal to my commitment, if we had met earlier, no one also would be able to take me away from her, so by that, I love her, but it’s late already as me and my wife has gone deeper and breaking up isn’t easy at these moment at all.

Recently, I found out my sales is already talking to different suitors which at times gives me bad feelings which makes me confused at the moment if I may loose her and this will definitely affect my business except I find someone better also.