Most Helpful Guy
They can't stand their partner's presence, they both know its coming to an end just like when they first had feelings for each other.
Most Helpful Girl
If they are a pussy:
- They start avoiding you (seeing you, making plans w/you, talking to you, etc)
- When you present them with a problem, they ignore it.
- When you try to talk to them about the relationship, they have no interest in it.
- When they don't respond to your attempts to communicate with them.
- You find out that they have started entertaining advances from other women.
If they have some class (& are at least somewhat mature):
- They tell you that they're not into the relationship, or they feel like it's run its course, etc
- They suggest an open relationship or any variant of that.
- They ask you if you see it going anywhere and seem very dejected at the possibility.
If you want to know if it's over, just ask them. Relationships end as soon as one person decides to stop working on them.