Has he been sucking for 2 hours or just lying at the breast with the nipple in his mouth sucking periodically? Make sure he is on properly - that most of the areola (especially the underside) is in his mouth. He should also be facing the breast directly (tummy-to-mummy), head slightly tilted backwards - you should be able to see his face.
When fixed properly and sucking effectively, he should not need to be on the breast 2 hours at a time to get a proper feed. He may be there because he likes it
Watch and listen when he feeds. He should initially suck quite quickly when he first latches on. As the milk lets down he should take long, deep sucks and you should hear him swallow as he sucks. As he gets to the end of the feed he will 'flutter suck'. Flutter sucking is good to continue for breast stimulation but it is also a sign that the feed is ending. You can choose to continue or if you have something else to do you could stop the feed. Babies should spit the nipple out spontaneously. If they do (my first ds never did!), wind him, change his nappy, then offer second breast. If he doesn't want it that is fine but do offer. Sometimes even the most zonked out baby will perk up for another go. Leave the nappy till after the first breast to change him because babies invariably poo when they feed (gastro-colic reflex).
If you feel he is lying there not doing much sucking gently blow on his cheek or stroke his feet. DEfinately try and learn to feed lying down. Babies just love being at the breast - it is not all about getting milk - it is being warm and secure, hearing your heartbeat and the lovely feeling.