Gonna try and do ME:LE platinum trophy in one go. Need advice

I have played all the Mass Effect games before, so I know what I'm in for. However I did miss out on some DLC stuff and it has been quite a bit of time since I played them.

I'm not worried about the Insanity difficulty on all 3 games. Actually, the advice I am looking for is Paramour on all 3 games. I plan on using the same character, and I would very much like to make the romances seem fairly organic and not seem like a player, but rather someone who has loved (but had to move on) or will continue to love the same character or characters.

The main difficulty will be that not all characters make repeated appearances, outside of maybe DLC (which I didn't play much of at the time).

Characters I am considering romancing are Jack, Miranda, Tali, or Samara, but none of them are in ME1, and I'm not sure if you can romance a few of them in ME3. Not sure who the best person to romance in ME1 would be that wouldn't feel like a betrayal in ME2 and 3.

Thoughts or opinions?