Dreams about ex-partners can often symbolize unresolved feelings or reflections on past relationships. In your dream, being at your ex's apartment with your current partner may indicate a juxtaposition of past and present, suggesting you might be processing your feelings about both relationships.

Bringing your old dog into the dream could signify loyalty and emotional connections you have with your past. Dogs often represent companionship and love, so this might reflect your feelings of attachment to that time in your life. Going through your ex's belongings and discovering pictures of you both could indicate a sense of nostalgia or a need to confront past memories.

Texting your ex about his dog suggests a caring nature and possibly a desire to maintain some level of connection or closure. It may also reflect your concern about how past experiences affect your current relationship.

Overall, this dream may be encouraging you to reflect on your past, acknowledge the emotions tied to it, and recognize how those experiences shape your current relationship. It might be beneficial to communicate openly with your current partner about any feelings that arise from this dream to ensure both of you feel secure and understood.