During certain missions, Wei will meet some girls he can date. After you finish a mission, you'll get the girl's phone number. You can then check your phone, look at your contacts, and call the girl you met. Doing this will start a side mission where you date the girl you called. Once you finish the mission you'll get a reward.

It can be very easy to skip over these dates which is why I'm making this guide. (Theres already a girlfriend guide on steam but its not in English)

Now, you may be asking "Who are the girls I can date? And when do I meet them? And whats the reward?"

Well, this guide will show you.
I won't talk that much about the date missions since they are pretty easy to finish, I'll just go over what you do and I'll link a video if you need a visual guide for one of them.

You meet Amanda during the mission, er, "Amanda".

Calling her will start the mission "Photograph Amanda"

You meet up with Amanda at Victoria Peek but you find out the park closed so you "convince" the guard to let you two in.

And then you do what the name of the mission says, photograph Amanda.

When you finish dating Amanda, Health Shrines will appear on your map.

You meet Tiffany during the mission, Club Bam Bam

Calling her will start the mission, Tiffany's Song

You meet up with Tiffany at Club Bam Bam and then you sing some Karaoke.

When you finish dating Tiffany, Jade Statues will appear on your map

You meet Not Ping during the mission, Listening In

Calling her will start the mission, Impress Not Ping
(Note: You can only call Not Ping after you date Tiffany)

You meet up with Not Ping over at Ping PC and then you walk over to the park.
Over at the park, you distract a police officer and then you hack a camera.

When you finish dating Not Ping, Cameras will appear on your map.

You meet Ilyana during the mission, Important Visitor

Calling her starts the mission, Make Ilyana Sweat

You meet up with Ilyana at the K-Bar, and then she challenges you to a freerunning race.

When you finish dating Ilyana, Lockboxes will appear on your map

You meet Sandra during the mission, Fast Girls

Calling her starts the mission, Fast and Hot Sandra

You meet up with Sandra standing next to the car she wants you to drive.
She then wants you to drive at high speed for 60 seconds. (Don't slow down, you gotta go fast)
After dating Sandra, new races will show up in Victoria's Peek

After you date Tiffany and Not Ping, you unlock an extra side mission called Red-Handed Tiffany.

Calvin will be outside of your safehouse in North Point, if you talk to him he will tell you that Tiffany might be seeing someone else.

You then go over to the payphone Tiffany uses and bug it. You then listen in to Tiffany's conversation and find out that she is meeting with someone else

After finishing this, the mission, Following Tiffany, will be unlocked.
Calvin will tell Wei that Tiffany is heading over to meet the other guy you heard her talking to.

You then head over to Tiffany's apartment and follow Tiffany to the meeting.
You confront her and then she breaks up with you.

After this mission, Not Ping will break up with you for seeing another girl, but she tells you to call back which could mean she's probably still Wei's friend, but it's left open for assumptions.
(This doesn't change anything gameplay or story wise)
(It does make the nightmare in north point story a bit weird if you assumed they stopped seeing each other, but that dlc is non-canon)

The only reward you get for these side missions is some face XP

Thats about it for this guide.
I suggest doing these missions as soon as you can to make finding collectibles easy.

Big thanks to the Sleeping Dogs wiki for all the info I put in here: http://sleepingdogs.wikia.com/wiki/Girlfriends

And thanks to the uploader of the videos I posted in this guide.