For 1 and 3 check out my "Reunion" list ;)
http://www.mangago.me/home/mangalist/48087/
2. Childhood friends:
http://www.mangago.me/read-manga/ano_hi_no_kimi_wo_dakishimeta_nara/
http://www.mangago.me/read-manga/elektel_delusion/
http://www.mangago.me/read-manga/kamisama_ga_yadoru_kotoba/
http://www.mangago.me/read-manga/ashita_mo_tanin/
http://www.mangago.me/read-manga/u_don_t_know_me/
http://www.mangago.me/read-manga/zettai_unmei_houteishiki/
http://www.mangago.me/read-manga/bokutachi_wa_asu_ni_mukatte_ikiru_no_da/
You'll find more on the mentioned list (the description will help you to get what you want)
Thank you very much!!
Yaoi manga where:
1. Uke and some are lovers but they broke-up, then after a few years or months, they got back together again.
2.. Uke and seme are childhood friends and they become lovers.
3. Uke and seme got separated for a long time and after a few years they reunited
3. Seme and uke have a relationship and they broke-up. When the person who initiated or started the break-up wants to be with his former lover again, that lover said it's too late..it's either he already had a new lover or he already move on.
~sorry for my english~