They "officially" met met in 2009 when they were introduced by Hailey’s dad, Stephen Baldwin. Hailey then spent years being a stalker/superfan who then turned sidechick/back-up girl. They married in October 2018 by accident, apparently not realising obtaining a marriage license would mean they were actually married. Three months into the marriage, Hailey spoke to Vogue about how hard marriage can be.
Rumours about Jelena started in 2010, and they became official in 2011. They couple has been creating headlines for years with their on/off relationship, finally calling it quits for good in 2018. Selena has recently come out stating Justin was emotionally abusive towards her.
In-between Selena reunions, Justin was linked to several girls. One of them was Sofia Richie, who dated Justin between August-September 2016. Justin posted several snaps of them to his Instagram, causing Selena to respond and making his fans go into a frenzy.
The Kardashians (Kendall, Kylie, Kourtney)
Justin has been linked to all three of the Kardashian sisters at various points in his life. His relationship with Kourtney, especially, generated a lot of headlines considering the age gap and the previous connections Justin had with Kendall and Kylie.
Justin apparently had a fling with Miranda Kerr back in 2012, causing the now infamous indecent where Orlando Bloom apparently punched him in the face. Did he deserve it? You decide.
The pair was spotted out on a date in 2016, but apparently things didn't go much further.
Justin and Barbara were rumoured to be hooking up while Justin was on a break from Selena. The pair were tweeting each other and were spotted hanging out on several occasions.
Justin and Shanina shared a lovely weekend together hanging out together in Las Vegas and Ibiza, but things never developed further. Shanina later revealed in an interview that Bieber 'loves the ladies'
+ lots of other Instagram girls, obviously
sources: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11