I agree that no one should be your entire world but there's a difference between "Solas you can't paint the walls anymore, the nobles don't like it, I'm taking away your paints." and "Solas you can't kill all the elves and call it saving us! The magical immortal who comes back from that might wear my face but it isn't me!" If his plan has the potential to cause Haven level destruction and mayhem then he should absolutely give that plan up and I don't care why.
I did make the distinction that, even if his plan is a bad one, he needs to figure that out on his own. Yes, his relationship with Lavellan can influence that realization, along with his friendships with Cole/Varrick/Bull/Cass/etc., the events of the game, and so on... but him dropping his plans just because he falls in love and wants to be with that person? I couldn't not see that as incredibly selfish (since I imagine he believes whatever he's doing is for the greater good and not for himself) and weak-willed (his plan, presumably, involves a vision of the future thousands of years in the making).
Edit: If he realizes he's being a stubborn ass and looking at it all wrong, and that maybe it's not his place to go 'fixing' the world, and you know, history of really bad screw ups and all, and gives up his plan for that reason, I'm all for it. Again, I just hate the idea of him dropping everything he's worked so hard for just because his girlfriend said so.