In 1860, Darla finds a mortal Drusilla and 'gives' her as a 'gift' to Angelus. He spends quality time mentally torturing her and killing everyone around her until he drives her to insanity, as well as a church, where she goes to take her vows and become a sister. He kills everyone in the church, has sex with Darla, and vamps Dru.
In 1880, Drusilla is feeling put out by all the time Angelus and Darla spend together and decides to make herself a companion. Spike becomes the fourth member of their terribly dysfunctional family.
Angelus and Spike do not get along but don't have to spend much time together anyways, because in 1898 he is cursed by vengeful gypsies in Borsa, Romania and Darla tosses him out on his ass.
He meets up with the three briefly again two years from then in China. He nearly gets his head chopped off by an infuriated Darla, who, with some convincing, agrees to give him a second chance. However, he distracts Darla away from refugees, barely hides his disgust when told of the Slayer-killing news, pulls Dru away from the refugees and then saves a baby from Darla's wrath.
Flashing forward to 1996 when Whistler finds him starving, living in sewers, and looking… well, it doesn't matter. He sees the Slayer for the first time from afar and decides to join the fight for good. In 'Angel', he kills Darla at the Bronze when it comes down to either her or Buffy. Season two, he meets up with Spike again and Dru and Spike realize he's not the same Angelus they knew. He soon loses his soul, however, and gets 'back together' with Drusilla… before going to hell.
The two do not meet again for a dreary four years until Lindsay calls in Dru to 'save' Darla from dying of syphilis. She hits him over the head with a shovel, he sets her on fire. Just like old times. *awww*
We assume they had a relationship from the 'pre-show' quote in 'What's My Line'. (( [the pre-show] is what Drusilla likes best, as I recall] )).
Gets soul-sick and by season 2 [BtVS] is downright Buffy-whipped so much so that he loses his soul in one moment's true happiness with her. Dives for Dru while Spike is stuck in a chair. Anyway, Angelus gets re-cursed with a soul and resumes following Buffy around like a lost puppy until moving to L.A.
Some brief sexual tension with JhaRa in Season 1 [A:tS] and sleeps with Darla in Season 2 with curious pregnancy results. Is currently smitten with Cordelia (( yeah, him and every other (wo)man alive )).
How dare you ask such a question! Here's a perfectly laid out BDS&M relationship ripe for the whipping. And don't just assume that Angelus is the one with the key. Drusilla has some heavy ammunition backing her up, as well as intimate knowledge from *decades* spent with the man.
'What's My Line' aka Bondage-Oh-Rama. Perhaps not too romantic, but seeing Angel tied to the bedposts with Dru between his legs pouring holy water down his chest gets five stars from me.
'Bewitched, Bothered and Bewildered', when Angelus hands Dru the heart for Valentine's Day. He knows just how to win a lady over.
Writing Drusilla as the weak female who cannot stand up to Angelus. Who allows Angelus to constantly beat the hell out of her when the mood strikes him. Not only have we seen no evidence to support this side of her character (( S&M tendencies aside, which is a whole different, consenting matter )) but we've also not seen this in Angelus' character towards the vampire Dru.