What should you do?

Aborting the overtaking manoeuvre is correct when you cannot be sure you can pass safely and completely without forcing anyone else to brake, swerve, or feel endangered. In German rules, overtaking is only allowed if the entire manoeuvre can be done without risk, with a clear view and enough space, and with certainty that you can return to your lane in time.

With a cyclist in an urban street, this often becomes critical because the road is narrow, parked cars can suddenly open doors or pull out, pedestrians may step into the road, and the cyclist might need to move left to avoid potholes or drains. Even if the oncoming lane looks free, you must also be able to keep the required side clearance (rule of thumb: at least 1.5 m in town, 2 m out of town). If you can’t keep that distance continuously, you must not “just go quickly” or “cautiously” alongside—you must wait and, if you already started, break off and fall back in behind.

Rule of thumb for similar questions: only overtake when you can maintain the minimum lateral distance, have enough room to complete the pass without speeding up aggressively, and can return safely without cutting in. If any of those points becomes doubtful, the correct reaction is to abort.