Should i go after a guy...?

...that already has a girlfriend but they seem more like friends than a couple to almost everyone? he even said that i made him reconsider his relationship with her and although he feels bad for flirting with me, he doesnt want to stop or doesnt want me to stop even though i told him i will if he really wants me to....he said he shouldve dated me a while ago when we both were single and he does tell me how he likes me and how considerate and nice i am so its not only physical