Romantic relationships are often thought to bring out the best in people. True love conquering all and such. I am not convinced that this is actually true though, and I think that more of the time they give people excuses for being awful than create good behaviour. It is easiest to see in the case of serious physical abuse since we all know that when we see someone with a black eye the most likely reason they got it is a blow from their romantic partner rather than anything else.
That assumption that it is okay or normal to pull all kinds of crazy out on your partner certainly holds true when there is no physical violence though. Jealousy in particular is something we often hold up as a virtue even though in non romantic relationships the idea of forbidding a partner to spend time with half of the population or demanding exclusivity would be shocking and bizarre.
This is kind of interesting when you consider it in the context of a monogamous relationship that is beginning to be polyamorous. In that situation many people seem to become the worst partners possible, making all kinds of demands and feeling justified in exploding over the tiniest issue. Ferrett wrote about this a bit and the very fact that he feels it necessary to clarify that being poly isn't an excuse to treat your partner like crap is very telling. We shouldn't need to make it explicit that blowing up at people you love over small misunderstandings isn't okay... and yet it seems we do.
Being in love with someone is powerful. It generates very intense feelings and those feelings can very easily be tipped over from adoration to hatred. While I love being in love and I think that for me it is definitely great to be in lots of romantic relationships we should recognize that these relationships don't automatically make us better people. Our feelings aren't magically correct and righteousness does not spring from romantic attraction.
Unfortunately we too often seem to think that romantic love removes the need for us to behave well and grants some sort of infallibility when instead it magnifies the need for consideration and good deeds.