1994 Chevy Corsica Confused

When driving the car, it feels like it is going to stall, so you have to take your foot off of the gas for a minute, and the hotter it is outside, the worse this is. Also, if driving over 45 miles per hour, the car shakes really bad. The Newest problem is, my boyfriend said he thinks it's the gas line? There was a leak and we couldn't start the car, it was already low on gas before this. He went and got gas and when he put gas in the car, all that happened was he got gas all over our driveway! What is wrong with the car. If it is the gas line, how much does it cost to fix that?