Scenario: At the age of 28 you look in your mailbox and find a wedding invitation. Yep, you are definitely at the age where you have been getting those more recently. As you open the envelope to see who is getting hitched this time you pause as your eyes dance across the name of your ex girlfriend and your friend written in timeless lacy calligraphy. Now, he wasn't your best friend, but in high school you definitely ran in a clique. You pause for a second...how should you feel about this? Is it ever okay for your friend to date or marry your ex?
Keeping that scenario in mind, we have decided there are a few factors that make this situation either messed up or acceptable.
As the old folks say, "Time heals all wounds" and so should be the same for any feeling you may have towards an ex. If you dated that person 4+ years ago and have had no romantic contact since you dated that person (i.e. Since you last had a title you have not had sex, been "talking to" or dating that person, you haven't been trying to rekindle an old flame with that person, etc.) then you should not be effected by anything going on in your ex's current relationships.
In addition, the longer you date someone the more serious you were about them therefore your feelings for someone you dated for 6 months are probably less serious than those of someone you dated for 3 years.
2. The Nature of Your Friendship:
In life we have different types of friends, those around permanently (best friends) and those around for a season (situational friends). A situational friend is an associate, someone you were forced to be around such as a coworker or team mate, or acquaintances. Situational friends have no serious obligations or loyalty to you or your feelings. You can not fault them if they choose to not have your best interest at heart or care deeply about your feelings when deciding on if they should or shouldn't date your ex.
3. The Nature of Your Relationship:
As we mature so do our romantic relationships. The seriousness and maturity of relationships varies from high school, college, and adult hood. There is a big difference between someone you went to prom with and dated for a year and someone you dated for a year and lived with at the age 25. The levels of commitment and interaction were deeper along with the criteria and credentials for deciding who you would choose to be in a committed relationship with. Therefore the nature of the relationship should effect your feelings on the situation. If you used to be serious you may feel awkward, if the relationship was short lived or elementary you should not care.
In conclusion you need to assess what your friend means to you and what your ex meant/currently means to you. Is this a matter of you being upset because your ego is hurt? If so, why is your ego hurt? Do you still have strong feelings for your ex?
...Marinate on those questions and you will have your answers.