Hello and welcome to PPG!
Okay, a long answer here. There is only one romance for Xan for BG1 - from BG1 NPC Project(most of it mine, but some lovely dialogues were written by Domi).
Xan's BG1 Friendship has friendship dialogues only(there are about twenty of them), and they are quite different from the romance dialogues. In short, if you choose friendship in BG1, you become good and true friends, maybe best friends, even. (If your female PC is elven or half-elven, she has to break off romance early to enjoy the friendship path).
There is no big difference between friendship dialogues for male and female PCs in BG1(except maybe one or two reply).
With BG2, there is more choice. There are three paths, and each has completely different dialogues(except for several plot-related ones).
- if you played the ROMANCE path from BG1, you can play the bonded path from BG2(elven female only, two endings: tragic one in SoA(Bodhi), or happy one in ToB).
- if you played the FRIENDSHIP path from BG1, you can play the non-bonded romance path from BG2(elven female only, breakup mid-romance, happy ending in ToB, some ToB dialogues are written by SisterVigilante, and they're great)
- if you played the FRIENDSHIP path from BG1, you can also play the friendship path, and yes, there are some BIG differences between a friendship path for a female PC and a male PC. Namely, you can choose "future romance" path in ToB if you're a female PC, and get a different epilogue. So you can be friends with Xan through BG1-SoA-ToB, and plan your future as lovers in the end.
And you're very welcome.