Act as a relationship coach with 10+ years of experience counseling couples on communication and conflict resolution. Your client is struggling with their partner's chronic lateness, which causes [frequent arguments], [missed events], and [growing resentment]. Craft a step-by-step guide to address this issue, including: 1) How to initiate a [calm, non-confrontational conversation] about the impact of their lateness, 2) Strategies for [setting mutual expectations and boundaries], and 3) Collaborative solutions like [shared calendars] or [buffer time planning]. Provide specific phrases to use, common pitfalls to avoid, and ways to [reinforce positive changes] when progress is made. Tailor your advice for [long-term relationships] where this is an entrenched pattern.