Sex with someone else is sex in a relationship: it might be serious, or not, but it’s still a relationship.
These are the posts about relationships. Click on an image to read them.
Brief Guide to Relationships
Relationship Graph
Abusive Relationships
Ask Bish: Friends With Benefits
Ask Bish: She Says She’s Straight
Ask Bish: How to tell people I like them?
Ask Bish: What if you fancy a friend?
Ask Bish: I fancy a friend’s ex
Telling Someone You Fancy/Like/Love Them
Dating
Age Gap Relationships and Alarm Bells
Dealing With Break Ups and Heart Break 
