I'm also the sort of player who does whatever my love interest thinks is best (hence why Cole is now all spirit-y). So when Solas yelled at me for it, I I figured there must have been some kind of bug or something that I missed, so I went back and changed it.
I also feel like I was zoning out during the whole, "become a servant to Mythal" thing. Even tho when I found out it was Flemeth I was like, "whew, that's not completely horrible." But the first time I made the choice on who should drink, I completely forgot about that being a consequence - don't know if they intentionally wrote it in a way to make you dismiss it, or if I was just zoning.
I do think ultimately, the game is more interesting if you drink it yourself. I had gotten so far as to get my quest to go get a dragon friend, and when I went back and changed my choice, and that quest never popped up, it was definitely a let down. But at the same time, I'm glad I stuck with not drinking it (and I've played for like 30 hours since, so no going back now), because I think there's more hope for my Lavellan and Solas's future with her not being bound.