Great link Qlippoth! Absolutely hilarious.
Tangential to and often overlapping forbidden love, there is the classic love triangle. There's nothing but pain and melodrama all around when the love triangle rears its ugly head. One benefit is that it's not hard to set up a love triangle were there is no clear "right" thing to do for anyone involved, and then you can always squeeze a mortal duel or two out of it.
Three tried and true love triangle idea seeds:
1. The betrothed: Someone has been promised to marry someone else, but then they fall in love (not with their betrothed of course). Political alliances are on the line. Families grow anxious. Intrigue and secret trysts ensue.
2. The dark stranger: The old, reliable, dependable love interest suddenly becomes less desirable when the mysterious, dark, stranger shows up on the scene. Sometimes people like a little danger, mystique, and excitement, in their romance. Of course the old dependable lover sees the dark newcomer for what he/she is, a callous user who plays with lovers like toys, and knows that what's really best for his beloved is for her/him to stay with him/her. To the partner, however, the dark stranger presents a whole new lease on life. He/she makes him/her truly feel alive in a way that the old reliable person never could.
3. The second life: Two people find true love. They become seperated and one of them believes the other to be dead. In truth the other person is desperately trying to get back to their soulmate (who is the only thing they live for in their terrible predicament). When the person who was presumed dead finally gets back to his/her beloved, he/she discovers that the other person has moved on to a new life, and a new love (add in children to really make things ugly).