I think that Holy Roman Emperor and King of Spain Charles V fits well what you are asking for. After almost 40 years of ruling his vast lands he progressively abdicated his ( numerous ) titles to his brother and son.

Tired, ill with several diseases and affected by the loss of several family members he finally retired in a monastery where he lived his final years.

Edward VIII abdicated the British throne in 1936 so he could marry Mrs Simpson.

Edward was known as a bit of a playboy Prince, he was rumoured to have had multiple affairs, but he met the American Wallis Simpson and evidently they fell quite in love, well clearly they did as he gave up the British throne and the entire Empire for her. Mrs Simpson was separated from her husband but legally still married (and already divorced once before), Edward made it clear that upon completion of her divorce he wished to marry her. The British government took serious issue with the prospect of the couple marrying as Edward as king would be head of the Church of England and Divorce was still viewed as socially unacceptable, also as head of the Empire his rule needed ratifying in the various countries ruled by the monarch and many reportedly were unhappy with the prospect of a divorcee on the throne (the Commonwealth still plays a part in the laws governing the ascension as they all agreed to a law change allowing Williams eldest child to take the throne even if a daughter was born first, so they aren't a pure formality and their opinions can matter). When Edward made his wishes clear to the then Prime Minister Stanley Baldwin that he did indeed intend marriage he was presented with 3 choices "Give up the idea of marriage", "Marry against the governments wishes", "Abdicate". He loved her too much to let her go, to marry against the advice of his government would back them in to a corner where their only choice was to resign and governments resigning is quite a bad thing, so he abdicated. He gave up everything for love which is quite romantic in it's own way don't you think. They lived out much of their lives in Paris where he eventually died.

As for sources it's pretty famous I thought it's even part of the plot of an Oscar winning biographical film "The Kings Speech", Wikipedia has it (since I checked the Prime Ministers name there), Google will be filled with it, there are endless documentaries and books.

King Baudouin of Belgium abdicated for one day in 1990 in order to avoid signing a bill which legalised abortion. He was a Roman Catholic and couldn't sign it in good faith.