Really? while he was overly harsh, I can't say I got that feeling at all. Nyarko kinda brought it on herself for completely acting up like she did, and while she had some valid points, it's hard to deal with them when she's always so crazy.
I felt like he was a bitch though. And not the good kind.
Hypocrisy at it's finest:
- She refuses to give him a straight answer whenever he asks her why she likes him; instead feeding him this "love at first sight" BS. What? His appearance is that attractive to alien asthetics? Granted, from what we've seen, that may very well be possible, but not in a good way (a lot of the males, females, and everything in between seem to want to make him into an unwilling gay pornstar). Nor does she explain what other traits he has that she finds attractive.
- She doesn't ask about his past or his dreams for the future, just imposes her own ambitions on him. Maybe the high school kid doesn't want kids at his age; ever think of that? She says in that episode that she tried so hard to become his "type"? Does she even know what his "type" is? No. She never asks him what he wants, and when he tels her what he wants, she blatantly ignores his wishes. I honestly doubt she even knows his favorite color.
- Whenever he tries to learn about her past; more importantly, her age (which will tell him if she is basically cradle-robbing or if he's the only one who will grow old if they do become a couple), or whether or not Lovecraft was accurate in regards to some of the nastier things he wrote about her/her race, she clams up or stops him cold. She doesn't bother to reveal anything about herself beyond her supposed "love" for him. This nearly bit them in the butt when her brother showed up last season. If he hadn't been so blatantly outclassed by Nyarko and so incompetent, he could have been a serious threat.
- More importantly, she's an alien lifeform whose culture, manner of thought (even her culture's definition of 'love' may be different from ours), biological development (does her kind eat their mates after sex; do they force the males to bear the young; does she lose control of her shapeshifting while having sex; this is all stuff he needs to know*), true age, and even her true form, are all unknown to him.
*No, really, he needs to know this. I remember one story in the Cthulu-setting (though it wasn't written by Lovecraft himself) where a very unfortunate prostitute found herself the target of a creature which absorbed and digested her; a process which it specifically referred to as making her into it's 'bride'; it even sent her threatening messages about the upcoming 'union' filled with 'marriage ceremony terms, and how 'pain' and 'agony' would be her bridesmaids. I wouldn't be surprised if he's read said short story.
I wouldn't be surprised if 90% of his hesitation came from the fact that she is from a species he knows nothing about save refrences by some famous author about them being very bad news for humanity (and 90% of the other aliens he's seen look very inhuman and act very insane), and she refuses to clear up any misunderstandings when does bother to ask. She's is very insistent, suspiciously so, on skipping straight to intercourse and reproduction, even after he saw her brother turn into something out of Legend of the Overfiend.
Yet, because she's cute and 'moe' (in her human form; she admits to 999 forms) and all that crap, he's the b*tch for thinking with his brain instead of his d*ck?
Dude, you sleep with her without learning all the important stuff she refuses to talk about. If you catch some crazy alien STD (not because you weren't her first time, but because something in her alien body reacted weird with the chemicals in your body), or she absorbs you into her flesh to be digested but still alive for all of eternity as nutrients for her future young, because that just happens to be what marriage is for her species, or she uses your union to open a portal to her homeworld for an invasion because your 'marriage' now makes it 100% legal by intergalactic law, you don't get to complain.
Yeah, it's a rom-com, so the above scenarios are unlikely in the extreme, but Mahiro doesn't know that and it doesn't change the validity of all of those points. Especially the parts about how he doesn't really know her, she doesn't really know him or even care enough to get to know him, and she clearly doesn't give a rat's butt about any of his plans for the future.
In real life, we call women like that stalkers with control issues, and we file restraining orders against them.
As it is, he almost certainly considers her a good friend, and no doubt feels indebted for her saving him. If she actually took the slow and steady "be his friend until we can become more" route, she probably would have nabbed him by now. He even admitted it when she lured him into the bath in her room.
Edit:
Just remembered that, at one point, she tells Mahiro that something about his appearance is unusually appealing to alien lifeforms; he just hits some sort of universal 'golden ratio' for them, which is why so many of them find themselves attracted to him or even want to kidnap him. So, it very well could have been 'love at first sight' if by 'love' you mean 'lust'. That makes it even worse. Granted, she may very well like his personality by now, but would it kill her to explain that to him when he asks?