I think my girlfriends cheatin?

i been with my girlfriend for 8yrs we still together but i think she's cheatin im unemployed due to a layoff since she got her job i guess the ppl she wrk around got her actin like she better than folks her family gets on my nerves cause they all r moving in wtf her sister marrage didnt wrk so she stay here also and my girl has a tendancy to show out round we go to the club she jumps up now n dance wit other dudes how disrespectful we argue all the time ill leave and go out of town for weeks she never ask me when u comin or nothin she doesnt care about me i been tryna make it wrk but im tired she been lying more too the only time she notice me is when she aint got no money thts it she became very selfish now im think about callin it off i made alot of sacrifices and i been thru hell wlkin out will be to ez help me out doc