Why does this taken guy with a long-term girlfriend keep pursuing me?

I met this guy who is in a relationship. (the time I met him i didn't know this) he's been pretty open about his situation which is pretty much he's been in a relationship with this girl for 10 years. he doesn't want kids now, she does - as he puts in their not 100% aligned on whats important in life. (whatever). he's been in this situation for almost a year - which is almost how long we've been talking very on and off (mostly off). I've told him i don't want to be friends and to call me if his situation ends and I'll let him take me on a date. Somehow he keeps coming back in some way shape or form feigning a desire for 'friendship' yet he is still in this situation, stating he is at a 'crossroads.' im sure its not the easiest situation for him, and one i can't understand - but if he is still in the relationship and cares so much why doesn't he just marry her? why won't he leave me alone? He has never crossed boundries with me, and is clearly not looking to hook up, but we aren't just friends either because we both admitted to having crushes on one another. I hope he just ends up leaving me alone and i find someone else lol - but why is he like this?

Why does this taken guy with a long-term girlfriend keep pursuing me?
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