"While he was still talking with them, Rachel came with her father's sheep, for she was a shepherd. When Jacob saw Rachel daughter of his uncle Laban, and Laban's sheep, he went over and rolled the stone away from the mouth of the well and watered his uncle's sheep." NIV translation
On the surface, this might look like Jacob has changed his ways and is finally caring for someone else but the key to understanding this is the fact that he saw not only Rachel but "Laban's sheep". He immediately saw an opportunity to get something out of the deal and he also wanted to impress Rachel because he found her attractive. He wanted to impress her with the fact that he didn't need any help to roll the stone away unlike the other shepherds.
"Then Jacob kissed Rachel and began to weep aloud." NIV translation
The kiss mentioned here was simply the way that people (especially relatives) greeted each other. The fact that Jacob wept shows his great joy and relief in making it to his destination. It is a reminder of the fact that he was still not sure that God would keep his promises.
That doubt is usually the thing that causes God's people to go outside of His will for their lives. This slight doubt lead us to think that we have to do something just in case God doesn't come through.
Before we are too hard on Jacob, we must acknowledge that the same type of thing happens to us who are in Christ. We must also remember that he didn't have too much experience of walking with God and he didn't have a lot of people telling him their stories about God. We have the benefit of looking back in history and we also have the written word as well as a great cloud of witnesses willing to tell us stories of how God has kept His promises in their lives.
Jacob had none of that and so we must take him as he is in this early part of his journey of faith. We should also be thankful for the fact that we live in a time and place where our faith can be built-up by studying God's word as well as by listening to the stories of those who have been where we are and faced the same struggles.