When a person (usually girls) stay with the first person they ever fell in love with, despite the other person treating them like crap. The more first times they had with the person, the worse the condition is likely to be. eg. If he was her first kiss, first time & first boyfriend etc...
Mika: Why is Sarah still with Jake? He cheats on her all the time, and she knows it.
Shirl: Yeah....she's got first syndrome pretty bad