Welcome. This idea actually cropped up as a joke between my closest, oldest friend and I, but the more I think about it the more relevant it feels. Maybe I'm wrong, but I feel as if most people in their lifetimes fall in love with at least one douchebag.
Douchebaggery does not come in one gender, nor does is come in one shape or size. Douchebaggery ranges in severity from the person who clearly doesn't care about your feelings and ranges all the way to that asshole who thinks physical violence is ok.
No matter the severity, being a douchebag is never ok. Each person deserves to be with someone they love who loves them in return. If you are a douchebag and you're being a douchebag to someone you love, take this time to reconsider how you treat them before they leave you.
A note on douchebags: Everyone does douchey things. Everyone can be a dick sometimes. This does not mean you are a douchebag. I know I've said and done things to my significant other that I felt terrible about and he's said and done things to me that made me feel terrible, but at the end of the day, he would never intentionally hurt me and I would never intentionally hurt him. Douchebags are people who either would intentionally hurt their other half or just don't care enough about them not to hurt them. They're people who are chronically inconsiderate of the feelings of others and aren't willing to make any self-sacrifice for their lover. We should never completely self sacrifice for someone else, but healthy relationships are filled with compromise without compromising self. Relationships may always be somewhat imbalanced, but the imbalance should never be so evident that someone always feels as if they are getting the short end of the stick. If they do and in fact are getting the short end- maybe it's time to reconsider.