Pema mentions "watching my soul mate spend his whole life with the wrong woman became too painful so...I confessed" in an ep.5...How is someone your soul mate if you're not romantically involved with that person? Big IMO, I can't help but think that sounds awfully conceited and naive of Pema. Tenzin did decide who he ultimately wanted for himself so that's fine, but should Pema really be giving that kind of advice to Korra and her daughters? Just look at what Korra did with it afterwards >___< Meh idk. It just sounds so messy.
You can still be deeply in love with someone, even if you're not romantically involved with them. Pema was shy, so idk, maybe it only happens with us shy girls. But I suppose more realistic people would brush it off as more like lust, or entitlement @_@ Pema was probably a believer in twu luv, destiny, and all that good jazz.

Or maybe she thought it was too painful to see Tenzin trapped with someone who was drifting away from him. Lin & Tenzin were both drifting, but situations like that aren't fun for either party. Plus he may have already had some feelings for Pema if one measly "I like/love you!" was enough to snatch him away.

Bah, ignore me @__@ Its nearly 9AM and I haven't slept at all..

I still agree with everything else you said though! (I could add to the list of reasons why I dislike Mako as of right now, but I babbled enough already XD'