Why He Stopped Writing To Me

Hello, my story dates back six months, I will be brief, I hope clear. I see a boy only for the purpose of non-committal relations from time to time, only in our country. He is bound, I am free, so it is more convenient for everything to happen in our country. At the time, he was the initiator of everything and it was a long time before I "surrendered". We see each other during the day for a few seconds, as we walk along the corridors of the university, I look forward to these moments .... but anyway. Our relationship is mainly writing emails and from time to time, quite rarely, a few hours spent we have. One time we quarreled in writing and decided not to write to each other again only if I wanted to see each other, but I couldn't stand it and wrote to him. He answered me, told me that he always had fun with me, that when we were really together we talked in a very different way. Sex between us has been going on for six months now, we've seen each other at least a dozen times. But the last time we saw each other, the next day he wrote me "it was very nice last night", I wrote him "I'm happy" and he didn't answer me anymore and so on for almost a week. I know that for him I am only a sexual object, I did not want or insist on more. I just wonder why he stopped writing to me, just like that Was there nothing to tell me or did I not react as he expected? We wrote to each other for six months and now suddenly it stops? Or did he probably get what he wanted and decided he didn't need me anymore? Guess a lot, but what could be real? It happened another time that he stopped writing to me and I couldn't stand it and wrote to him and he thought he had problems, but for a long time our conversations were meaningful and we discussed common things, related to the university. At first I remember that he had stopped writing to me in the same way and then said that he had done it so that I could ask for it, but then we had not had sex at all, and now it has happened after we had done it again. . It still seems to me that men cover in this way after sex for the first time, not after a six-month meeting. I am asking for advice.