Since I don't want to post 4 different questions, here are the type of relationships I'm looking for:

1. The SEME has a girlfriend/wife, but starts a realtionship with the uke (Please HAPPY ENDING, so it would be nice if he leaves her for the uke).

2. The SEME is a (straight) womanizer, but, out of curiosity or something, sleeps with the uke.

3. BOTH seme and uke have a girlfriend/wife.

Seme sleeps with BOTH the uke and the uke's girlfriend/wife
OR
Uke sleeps with BOTH the seme and the seme's girlfriend /wife
(not at once and it doesn't have to be in that particular order)

Also pleeeeaaaaaase ONLY HAPPY ENDING! It can be sad while it happens, but I really hate sad endings!!
Yeah, I might be a little messed up in the head from so many yaois, but I guess I really like it when the seme and the uke are straight, or at least the seme 😛

I hope I am allowed to post so many requests in one post, but I didn't wanted to post 4 different questions (and they do have the straight seme with girlfriend in common). But if I am not allowed, please tell me and I will delete the post 🙂

Thank you a lot!

I do not know if this is really what you are searching for, so sorry when it wasn´t.. :>

Regarding your first question:
Boku wa Kimi no Tori ni Naritai
is like that, but maybe you know this manga already. If not, i can recommend it, it´s cute 🙂
Allure
is also similar to the theme you asked for (I´s been a while since i read it, so i´m not sure anymore if it was the uke or seme who was in a relationship..but i remember it was wonderful and sad)
Ikoku Irokoi Romantan
here it was definitely the uke who had a fiancee; it´s a pretty well-known manga (maybe you read it already) & there is an anime too

The curiosity theme:
Himegoto Asobi
one of the best works out there regarding this topic, i think 😉 (but not completely translated/dropped by the author, i don´t know but it´s a shame! -.-)
Happy Ending
wonderful, peaceful manga, but also very sad; i´m not sure it fits your idea of a happy ending..
Suzuki Tsuta deals in some of her works with this theme, too. In my opinion she´s always worth a read 😉 Suzuki Tsuta

Regarding the "both have a girlfriend"-theme, i read a manga that dealt with something like that, the protagonists had a strange sex-friendship, but also kept their girlfriends... I can´t remember the title tough, i hope it will show up somewhere (maybe here?) ^.^

I really love sleeping... but I love Yaoi more! -.-

Koi ga Bokura wo Yurusu Hani by Motoni Modoru - fits the #3 category (might even be the one readallthemanga!! mentioned)
It's been a while since I read it but I think the ending can be considered happy, its sometimes hard to tell with Motoni Modoru.

For a more comedic take on the #3 category, 50X50 by Kunieda Saika

Let's see...I think Kyuuso wa Cheese no Yume o Miru kinda fulfils #1, and I'd definitely nominate [Bónd(z)](http://www.mangaupdates.com/series.html?id=3810) for #3. Doushitemo Furetakunai sorta matches #2. Hope this helps!

Check this thread out - some of these will fit what you are looking for in at least one of the 3 areas

[url]http://www.mangaupdates.com/showtopic.php?tid=37706&page=1#post575417[/url]

Firstly I wanna thank you for the title you already gave me 🙂 Also BUMP!

Junjou goes with your #2 request.
Nigai Kajitsu, the first story goes with #1 and the second story goes with #4. Though I gotta say the second story is pretty messed up so it really depends on your taste if you like it or not. It was....unique.

Also you might wanna take a look at this if you want more of #1 😃

[img]https://31.media.tumblr.com/fed8f641faa089fa16ee883f5b18f006/tumblr_n09tpwWCYW1qk16e0o1_500.png[/img]
K n e e l .... This is the difference between your and my eye-level.
Rai from Noblesse