Nexus Card with Flagged Passport

Hello,

I wondered if anyone has any experience with this particular issue. I traveled to Canada last June to stay with my boyfriend for four months. I brought with me (stupidly) a car full of clothes and kitchen items (he'd just moved into an unfurnished place) as well as necessary equipment for me to work from home such as a desktop computer and a printer. We were pulled in for secondary screening and explained our situation to the border agent who inspected the car and told me that I'd brought too many of my things for four months and that I did not have substantial ties to the US (I own my own business but do not own property in the US, nor was I renting at the time). He advised me to return to the US and come back the next night with significantly less baggage and he would let me through. I was given a form to withdraw my application to enter Canada and was allowed entry the following evening. Since then, I have returned to the US and drive up often to visit my boyfriend. Each time, I am pulled into secondary screening and interviewed about my file (how the relationship is progressing, what we plan to do in the future, etc.). I know that I am pulled in each time because my passport is flagged due to the denial of entry a year ago. My question is, will this be an impediment to my receiving approval for a Nexus card? Does the denial of entry constitute a violation of Immigration procedures?

Thank you all for your responses.