Dreams involving past relationships and significant emotional experiences can often reflect unresolved feelings or concerns in your waking life. In your dream, seeing a photo of your ex-husband and his mistress may signify lingering emotions related to your past relationship or feelings of betrayal. The tablet belonging to your son could symbolize your connection to family and the impact that past relationships have on your current life.

The act of logging into your ex's Gmail account and finding emails could represent a desire for clarity or truth about the past. It may suggest that you are seeking closure or trying to understand your feelings regarding the end of your marriage and the dynamics that followed.

Consider the following insights:

1. Processing Emotions: Your dream might be a way for your subconscious to process feelings of hurt, betrayal, or jealousy. Reflect on how these feelings might still affect you today.
2. Trust and Security: The discovery of the emails indicates a breach of trust, which could mirror concerns about trust in your current relationships or in your life overall.
3. Fear of Repetition: If you've moved on, this dream might signal a fear that similar patterns could emerge in your new relationships.
4. Desire for Closure: The dream could indicate a need to confront and resolve any lingering feelings regarding your ex-husband and the affair.

To move forward, consider journaling about your feelings regarding this past relationship, discussing them with a trusted friend, or even seeking professional support if needed. This can help you find a sense of closure and allow you to focus on the present and future.