My answer to this question is different now at (mumbled age) than it would have been in my 20s. At this point in my life.....after a good deal of battle scars & the healing of a dinged up spirit....& the wisdom that comes with living through an unhealthy relationship my answer is that it's both. I believe that that wonderful, amazing, "omg this is the most amazing person ever!!" feeling that we get initially as we fall helplessly through a field of flowers & rainbows is our heart choosing on its own who we fall in love with. Now, in my 20s, that was enough for me to commit myself to that person for life & we would just figure out how to deal with marriage, spirituality, how we wanted to raise our children, etc., etc., down the road....whenever! Because who wants to let reason come in & mess up the rainbows &; fireworks of that high we get when we're falling in love!? Well, for one, ME IN MY FIFTIES!!! I think that sometimes we can't help who we fall in love with.... But we can - & >should< - choose who we are going to spend our life with. There's where the wisdom I've gained through the school of hard knocks kicks in. I had the rose colored glasses knocked off of my face & crushed into the dirt by a couple of people that I "couldn't help it I was in love with!". Now, at this wonderful stage in my life? I will not allow myself to spend a week in a committed relationship with someone that doesn't cherish me in return...let alone a life time commitment. And - I would want to know that my partner is wise enough to do the same.
So...I don't think we choose who we love... But, if we're smart, who we commit ourselves to ..is a choice.