I think my boyfriend is cheating...can you help?

okay so this is the deal my bf has been acting odd lately. like today we was sup post to pick me up after going hunting. he said he was going to text back and he did saying he was going to santa fe. after that he wasn't texted back. that was around 11 am and now its 7 pm. he accidentally called me and i heard him talking to another girl. this is the 2nd time its happened. i hav had this feeling that hes been cheating for a while now. he's also been blaming me that i hav been messing around when i havent been. i think he's been doing that just to put his guilt on me. i need ur help...wat do you think...am i just over reacting or do you think hes messing around?