If you're looking for manga similar to Itsuwari no Tsugai Keiyaku, you might like these titles.
In the Omegaverse, alphas and omegas are born into two different worlds. While alphas excel in life, omegas are treated as scum who lure alphas into mating. Sousuke Tsukigase is a blissfully naive alpha until he falls in love with an omega, Jun. From then on, Sousuke frequents the brothel of Omegas where Jun works and starts questioning himself and the world he knows while he quickly approaches a fork in the road: lead a typical alpha life full of success and stability or take the road less traveled.
"Ken, do you really like me?" Kengo is always a little dry with his girlfriends, and that's what they say when they dump him. Then one day, he sees his classmate, Chiaki, dancing in high heels as part of a cultural festival presentation and gets a hard-on. He thinks it must be some mistake...... Depressed, but on his way to the after-party, he sees Chiaki going into a hotel with a strange man and finds himself further obsessed. Unable to contain himself, Kengo confronts Chiaki and...... What is this dark emotion......? A clumsy, straight, antisocial boy and a beautiful, gay, self-prostituting boy. A criss-cross love between male students muddled by infatuation and lust!!
Fifty-five dollars for sixty minutes. That's my worth for today. Employed at a male-oriented escort service, Masaki works under the name "Miyabi." Though the job is challenging at times, Masaki is motivated to do his best so that the staff member who hired him at his lowest, Mr. Ichikawa, will praise him. Teased day in and day out by sexually frustrated customers, Masaki's body grows ever more sensitive...
Boyfriend service Stray Cat's most popular employee, Haru, is known for his pampering skills. When he gets going, he turns into the sweetest "boyfriend" for his clients. Wanting to learn how to feel good in bed, Hiroki works up the courage to call for Stray Cat's services. That's when Haru appears at his doorstep and shows him a night he'd never imagined... Hot, steamy action ensues both in and out of bed as this flirtatious night worker and his cute, sensitive client find themselves getting attracted for real...!
Akito Kisaragi is a prostitute trying to survive in a world where omegas like himself are considered the lowest rung on the ladder of society. Abandoned by his mother at an early age and forced to use his body to earn his living, Akito didn't think his life could get much worse - until he is drugged and kidnapped by human traffickers. Sold at an auction for an exuberant amount of money, Akito falls into the hands of a wealthy alpha named Reiji Asahina. Reiji tells Akito he purchased him due to the Kisaragi family's well-known high fertility rate, and only wants one thing from him: to give birth to his child!