ADHD signs for an 8 yr old or behavior issues only? help!

Im hoping someone can give me some insight, i'm at my wit's end! Here is a brief background...My fiance's son is 8yrs old, he stays with us every weekend and one day a week, more during summer vacations. His ex wife and I get along great, and she encourages me to help care for him. He has been in my life going on 3 years. His Dad, (my fiance) tries to be more of a buddy than a Dad, which i think has contributed to some of the issues. This child is very creative, social and can be the best little guy you would want around....but then there is another side that is wearing us down. He talks back more than not, has meltdowns when things don't go his way, will not do his homework to the point of throwing papers, pencils, pouting, crying, saying homework isnt fun or fair, wants dad to do it for him, but Dad won't thankfully. If we are doing something he enjoys, he is fine, as soon as it is something he isn't crazy about, he will turn it misreable for us...like when we were at a outdoor festival, he had the choice of watching a movie they had with other kids or staying with us...he had his dad walk him over to the movie, only to change his mind and stay with us...TWICE...and then acted out while with us, complaining, crying, sitting on his Dad's lap and squirming, saying he was hungry and wanted to leave but wouldn't eat the food we offered him until we finally left out of frustration...then he was fine, until we said he was going to bed early, then had another meltdown saying he wanted to go home to his Mom and when i trried to talk to him he told me "not to talk to him".

He interupts our conversations, can't sit still, has a hard time staying focussed, we have to tell him the same things over and over and his favorite words are "I forgot". he lies about eating all his dinner to get dessert, about brushing and flossing and can't accept losing in any game. he acts like he is 8 going on 18 at times and other 8 going on 3 others. It is frustrating for us, he is not spanked by his parents and he wants for nothing. I feel he should be tested for ADHD, especially since his Dad has it...but they have not done that yet. Any suggestions on how to cope? I can only do so much, I am not the parent, but he spends haldf his time at my house and it is getting to the point where I don't want to see him at times...I love the boy, but his behavior is stressing me out. Thanks so much!

[jdtm]

I feel he should be tested for ADHD, especially since his Dad has it...

Big red flag!  I would think the first person to contact would be his teacher at school.  This would be the "job" of his father and/or mother.  All the best ....