Is what we are doing wrong, despite being fine with it ourselves?

There is this guy I have known on and off for about 4 years, we met when I was 14 and he was 18, we had loads of mutual friends and he went to the school I went to. He was always a bit arrogant and stuff, but anyways, he was interested in me, and we started a relationship, not a proper one, we weren't even seeing each other i suppose, just occasionally, like really rarely when we were both free (which wasn't often) anyway he went to university 2 years ago, I haven't seen him in over a year but we still talk sometimes, we are always promiscuous and I lost my virginity to him, we were quite good friends, but we have never been exclusive, we are just each others flings. I know I shouldn't but there will always be a place for him in my life no matter if he or I are in a relationship with someone, It's like meeting an old friend, but just on a physical level. This must be wrong, but I don't particularly want to stop it. Is that just me being easy? we both understand what we want from each other, and it's not much, it's just nice to know there will always be someone there. I don't plan on seeing him any time soon, but when he's back from uni we probably will meet up, especially since now I can go to bars and clubs, which was the main reason we didn't really see one another that much. Is this an unhealthy relationship even if we are both completely understanding of each others needs?