How to deal with the guilt of ur SO finding out you relapse

About a year or two ago I stopped cutting on a regular basis but I relapse last summer. Still I only end up doing it like once or twice a month sometimes none so it's a lot better then when I used to every week. However my SO found out almost right away that I relapsed. She used to cut as well but I'm so proud of her that she's gotten past all that and is doing a lot better mentally. However I'm still not well and miss cutting like I used to but they keep finding my cut marks and feel sad for me. A week ago they went on a trip and won't be coming back for another week (2week long trip) but I'm going through a really hard time and feel the urge really bad. Before they left on the trip they asked me to promis them I wouldn't hurt myself while they where gone but I feel like I'm at my limit. What am I supposed to do or how can I deal with the guilt of them finding out I did it.