Such a strange situation so why does he bother?

i have been seeing this guy for 15months now, i enjoy his company when he is in a good mood but he also annoyes the hell out of me :), i see him about 2-3 times a week, we argue, laff, watch tv, have sex, we just like an old married couple without the relationship title. i no deep down it isn't going anywhere, but i do like him and enjoy what we are doing together at the mo, my issue is... he doesn't treat me as a friend would do, he always makes me wait before replying to texts, if he bothers at all, i no he is on dating sites and actively seeks other woman, more recently i had some inside info regarding a lady who is dating a friend of mine who said he kept leaving his number etc but she isn't interested, so if this is the case why does he bother to carry on spending time with me? if we fall out big time he really makes the effort to make up, being really nice, offering to feed us, providing film and drink etc why does he do this if it isn't what he wants? is it because im to easy? im thinking of finishing it after hearing about this recent incident, but im not sure what to do :(