To dare put such a huge question into one sentence...
I love God because He loved me first.
To expand a little, from 1 sentence to a short story...
Why do we love anything we love? Countless songs & stories have been written about falling in love, and quite a few of them marvel at how love can come without any idea why.
In that sense, my love for God is like any time I've fallen in love with a girl. Yes, there are traits of God I can point to, many of which give me reason to try to maintain this love. There are also traits of God, particularly in regards to prayers that don't seem to work & problems with Christians, that make me doubt this love. But commitment is a noble thing, and understanding every detail is never essential to staying in love. I see His commitment in the Crucifixion, in the Incarnation, in every covenant & blessing & action He didn't have to do, but He did for us...for me. I see the Gospels as historically accurate accounts of a real person, I see the Resurrection as proof of the greatest claims a man ever made (not an apologetics thread, but look up Cold Case Christianity to see the evidence for yourself), and if any man--particularly if the man is God!--is willing to suffer, just so I don't have to suffer alone, then that man is at least worthy of my respect, and love comes naturally over time.