By Tony Owusu Spirit rejected JetBlue’s improved offer, which included a $200 million breakup fee, and is now on track to merge with Frontier. There’s a reason for an engagement period before a wedding. The engagement gives both parties a chance to make absolutely sure that a life-long commitment is what they want. While JetBlue (JBLU) – Get JetBlue Airways Corporation Report and Spirit Airlines (SAVE) – Get Spirit Airlines, Inc. Report were never officially betrothed, in April, Spirit agreed to talk to JetBlue about its unsolicited $3.6 billion takeover offer. At the time, Spirit had been pla…