I'm surprised so few people play like this. I never felt comfortable taking a romance option in ME2 if I already had one in ME1 (unless, for storytelling purposes, I choose to let them die on Virmire, and even then due to storytelling I usually have them reject even the ME2 characters out of guilt), but this is how I imagine Shepard to be (at least if he's a Paragon; Renegade!Shep would likely not care about commitment), and I like how well you wrote it. Shepard cares about his crew, but remains faithful to the one he fell in love with despite the argument - that's how it should be.

Great job!

update please more tali and shepard