Teenagers! ! Help!

Well I have had yet another horrid weekend with my stroppy 12 year old son (13 in January ) and I'm worried he's driving my boyfriend away. The man in my life is the best thing to happen to me, he's kind, generous and I love him lots. My son on the other hand is rude, obnoxious, selfish and generally unpleasant . I can not understand why he's behaving like he is. I'm not soft on him and he's disciplined for his bad behaviour. He never used to be like this. He's never had a dad and I wonder if its jealousy but he likes my boyfriend but is also rude to him at times. Has anyone got any suggestions? We hope to ttc soon so I need to deal with my stroppy son quickly.

Please only constructive comments, no rude ones, thank you x