Why does he still want to be friends?

I'm married with a divorce filed still sitting at the courthouse waiting for processing. My crush I guess has a college girlfriend and they been together for 2 months. I secretly liked him before he got a girlfriend, but hide it real well and he didn't know. A month into his relationship, he found out I like him. He flirts with me and it seems like he likes me back too. I always tell myself he now has a girlfriend but one day it got pretty hot and heavy and we ended up having sex. We still talk like normal a few days afterwards then suddenly he told me that he didn't feel right doing this to his girlfriend, and that he needs to respect her more, and he wishes it never happen. He wants us to be just friends we can flirt but no sex. I told him no I don't think being just friend with him will save my heart from breaking, it'll just make the pain worst. But he begs me to please be friends with him he promises he really cares about me and don't want us to be strangers. I finally said yes we can be friends. I'm confused as to why he want to be friends still of he isn't gonna date me? And I don't even know if it's a good decision to stay friends with him because it'll jusy break my heart more. But deep down I really don't want us to be strangers either. I really do like him a lot still.
Why does he still want to be friends?
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