http://www.mangago.zone/read-manga/blood_strangers/?PaGJ
sorry,, I can only think of this...
I think you'd enjoy Vassalord! It does have some suggestive scenes that are almost yaoi but not really because they're vampires taking a meal but yknow how that goes...
Silver Diamond too, it's tagged shounen ai but there's never anything to really show for it so it's basically a bromance.
This isn't supernatural in any way, in fact it's slice of life, but Nanohana Boys is a great story and with a very strong friendship that gives totally bromance vibes.
A manga /manhwa/manhua similar & same vibes as I-ren, Bloody Mary(SAMAMIYA AKAZA), and Vampire Library. It's not just vampires it can be anything supernatural & fantasy...it's like Shounen Ai vibes too cuz the 2 male mc are very close in a way that their soulmates, not necessary to be a couple or anything but the Bromance is Loud & I love it hehe