I'll 2nd Irenicus suggestions, all very good stuff.
Minamoto-kun Monogatari - currently running series that deals with a guy trying get laid with 14 different woman including his extremely hawt aunt
Chapters are short tho at usually 8 pages long and it's up to chapter 16 atm I think.
Koibana Onsen - A pretty good romance story set at a onsen where I guy visiting falls in love with someone that works there.
Plenty of action to be had and all in all very nice.
Completely finished series.
Toshiue no Hito - Good romance about a guy and a young looking but older girl, pretty good stuff alraound here altho can't mind if the scans finished as I haven't read this in some time(which I'll need to get round to doing some time)
Henkoi! - ehh from what I can remember it's got sex....I think, well it does involve highschool kids but it was actually quite nice cause it was a simply enough story about a couple that did actually like each other and while yes there were obstacles and such, it's a nice story expect maybe the last chapter.
Very short at just 9 chapters if I recall and pretty sure there will be a few "fetishes" in there somewhere.
Basically a very borderline h series but one I actually liked.
Pink de Pink - pretty simlar to
Henkoi!, highschool kids again and ghosts if I recall right.
TBH I can't really remember this very well but I think it fits with what you want.
Theres something that comes to mind, think it was called Gakkun Heaven or something like that.
Well it's about a teacher at that gets involved with another teacher and some students, I think it was he knew the teacher from before and that was the reason he became one I think.
Anyway I didn't like it, all I can remember is that it's all just too daft for my liking, everyone was plain stupid in it but I'll suggest it anyway, you may like.
Actually there are quite a few of these borderline H series that could fit but at same time not really fit, it's almost always the same thing with sex in every chapter and lots of sleeping around with different partners, whether or not you can say thats romantic in the least(as these series tend to gloss over cheating and rape and stuff) it's all there in essence.
I'd suggest maybe having a look at the Categories Boderline H tag on Mangaupdates.
On that note probably best to give up on the Gakkun Heaven or whatever it's called I mentioned above and going for some others that are better.
Virgin na Kankei and
Glass no Megami are 2 pretty similar series to each other and better than the one mentioned abovew but even still not great.
Really tho with these types of series(mostly the really borderline stuff) you can't really expect much.
I'll need to do some digging around on these, I'm having a nightmare trying to remember this stuff>__<