Communicate with the other person and see if something can be done to improve the situation. If not, leave on the best terms possible.
Talk it out. Especially if y'all been at it for a minute. It's always best to be transparent with each other.
Petition for this to be
Communication is key. If you can’t do that it won’t work. Leave.
Talk it out
See if you can fix it
If not
Then just leave
Depends what I'm unhappy about. If they start acting strange I talk to them to see what's wrong, I try to help. If they start mistreating me then I tell them about how they hurt me, and see how they feel about it and why they're acting this way. Cheating/Betrayal is an automatic end to things, no excuses can justify it imo.