Mass Effect 2
Things get more complicated in this second episode. If you continue the adventure with the same save as Mass Effect 1, your romance will be imported and preserved.
The original three romances are currently not part of the crew, but a portrait in your bedroom indicates your bond in love. If Shepard develops a romance with a new character, the portrait is going to be shot facing the wall, and this will negatively impact the original relationship in the third episode, even if it is possible to reestablish it.
If no romantic relationship is developed with the new crew members, the reunion with the romance of the first episode will be with a kiss. Shepard will also look fondly at the portrait en route to the suicide mission, instead of warming the sheets with their new conquest.
Please note that all crew members, and even Shepard, can die during the suicide mission at the end of the game depending on your choices and actions. This is generally seen as a bad thing when it comes to maintaining a romantic relationship.
As in the previous game, you have to respond favorably to the dialogues with the character you are courting, and choose the options that show your physical attraction during the dialogues. It will be important to complete the chosen crew member's Loyalty mission so that you can make your romance a reality.
If you officially enter a romantic relationship, but still charm other crew members, a showdown will take place and you will have to choose between them. But be careful, you will lose loyalty to the person you are going to abandon -- which is clearly not a good thing, especially if their loyalty mission has already been completed.
Unless you deliberately want to create dramas at the risk of losing characters permanently (to explore the whole game), we strongly advise against it.
Romances exclusive to male Shepard
Miranda Lawson: Your liaison officer with Cerberus is obviously a very alluring romance.
Tali'Zorah: The Quarian technician from the first episode is back, and now a possible romance.
Jack: Be careful, Jack will offer to sleep with you from the first dialogues. This is a trap, accepting will not unlock the Paramour trophy, and it will completely block all possibilities of romance with this character afterwards. You must therefore refuse the intitial advances.
Romances exclusive to female Shepard
Jacob Taylor: The male counterpart of Miranda.
Garrus Vakarian: Another returning first-game crewmate. Romance is possible this time around, especially if you enjoy scarring and calibrating the ship's cannons.
Thane Krios: This assassin is encountered on the planet Illium during the second wave of crewmate recruitment. Better to go get it quickly if you want to start a romance.
Liara T'Soni
Originally reintroduced via a DLC by the name of Lair of the Shadow Broker, Liara can be found before or after the end-game suicide mission. She automatically knows whether you've been unfaithful or not, but you can choose to preserve her romance, even If you've started a relationship with another Mass Effect 2 character.
It's also because she has a big heart that Liara is the best. You can also choose to end your relationship. Either way, it's possible to have sex afterwards with another romantic interest before the game's final mission.
Other romantic interests
In addition to the characters above, you can show your interest in other characters, but they don't count as true romance and they don't grant the Paramour trophy.
- Kelly Chambers: If you show interest in Kelly and invite her to dinner, since you have no other romance, she will come and dance for Shepard. If you really like her, you can start a relationship with her in Mass Effect 3.
- Samara: If you play a Paragon Shepard, you can manifest your feelings after her loyalty mission, but her position prohibits her from returning the favor. Be aware, however, that it will eventually be possible to start a relationship with her too in Mass Effect 3, so it's not lost.
- Morinth: You can attempt to have Asari sex with Morinth during Samara's Loyalty Mission, but the result is fatal for you. Likewise, you can choose to have this relationship after the suicide mission if you survive, but the result is death again. Unlike previous characters, she never becomes a romance option for some reason.
