I've just downloaded and Installed the Imoen romance mod and I'm in the installation phase, it's asking:
Install Component [Romance Option]?
choose one:
1] Allow Multiple Romance's
2] Don't Allow multiple Romance (Only valid for Vanilla romances)

I have a vague idea what this is but can't find any clarification anywhere, can someone tell me what this option changes?

Basically, if you would like to be able to romance Imoen alongside the original BG2 romances (Aerie, Jaheira, Viconia and Anomen) without any of them complaining, pick option 1. If you would prefer not to, pick option 2. What the () message in option 2 means is that if you have installed any other mod romances (like Nalia, Keldorn, or custom OCs), they will all still work because the Imoen romance mod author isn't able to specifically script to block those from happening.