Fumi no semi and gakuen heaven both contain BL. Both stories are very touching and emotional, especially 'Fuyu no Semi'. In both animes the love between the main characters are very apparent. Gakuen heaven is a very tamed shounen-ai anime. Fuyu no Semi has a very good plot with action, war, romance, separation and finally eternal love. In both anime there is separation.
However gakuen heaven, being a sweet sweet and happy go-lucky BL anime, does provide with lots of entertainment. Fuyu no Semi is more realistic in terms of deeper emotions and separation. Fuyu no Semi is dammed touching, especially the last part.
Watching both anime will be a great experience.