16 year olds and stepfathers "problems"?

I have a 16 year old son. He is very emotional at times and has been through alot over the past couple of years with his father and my divorce. He is a good kid and has a good heart. He does have his problems but don’t they all. My fiancee though thinks he should be more adult says he is lazy and doesn’t want to learn. He does have learning disabilities but is a smart kid. He hurts my sons feelings alot and when my son gets angry and confronts him which usually turns in to an all out war my fiancee goes off. He says alot of hurtful things. He says my son doesn’t respect him but he does and yes he is the typical 16 year old with an attitude at times. But my question is what are most 16 year olds like? And what should i do to ease the tenion in my household between the two?