If the lawyer obtained confidential information from you that may be relevant to the current representation, I see a conflict of interest. Even if you are not a party to the present action, your fiancé is a party and you are likely to be called as a witness.
My opinion is that if you were married to your fiancé it would be a clear conflict of interest, but I still see this as a conflict of interest that would support a motion to disqualify the lawyer because he is assumed to have obtained confidential information when he was your lawyer.
I think this violates Rule 3-310
(B) A member shall not accept or continue representation of a client without providing written disclosure to the client where:
(1) The member has a legal, business, financial, professional, or personal relationship with a party or witness in the same matter; or
(2) The member knows or reasonably should know that:
(a) the member previously had a legal, business, financial, professional, or personal relationship with a party or witness in the same matter; and
(b) the previous relationship would substantially affect the member's representation
(E) A member shall not, without the informed written consent of the client or former client, accept employment adverse to the client or former client
where, by reason of the representation of the client or former client, the member has obtained confidential information material to the employment.
I hope this information is helpful.