Warning: This a hentai review only +18 (depends on your location) should read this:
Musuko no Tomodachi ni Okasarete AKA The Cougar Trap
First of all this is one of the best box art I've ever seen.
Two families of mother and son living next to each other in the same apartment. The mothers are lonely wives who have not had sex in ages. You know where this is going right? Apparently the sons go to school at day and by night, the sons have sex with each other's moms (kind of funny when watching it). The ending really suprised me, watch it so you'll know what I
mean! Overall I liked it, even with the incestious content.
Conclusion: Definitely fap material!