How many starts is too many?

My bf of 3 yrs and I have stopped seeing each other two times because of issues related to his behavior with friends and girls. Last Nov. we parted when I'd had enough watching him flirt with his guy friends daughters. He has a fun personality and is liked by everyone. We were having dinner with one of his friends and while my bf was at the buffet talking to his friends 15 yr old daughter, the friend we were having dinner with called her his second "girlfriend." Her dad owns the restaurant. He returned to our table and shortly thereafter popped her with a towel she was holding to clean the booth near us. I told him later I thought his behavior was inappropriate. He denied knowing what his friend meant about the 2nd girlfriend comment. In May he called, missed me apologized and asked for another chance. Things went well for about 4 wks and then I found a number of porn and dating sites in favorites on his computer. Said he hadn't visited the dating sites in months even tho they were in his last 3 days of viewing. Said he'd only been looking at the porn since wed gotten back together. I don't care for the porn but am hurt over the dating sites since he's the one who came back to me promising to be different. We live over an hour away from each other so my trust is being challenged again. Should I believe what he says or run for good. Hes a major charmer with words. I'm 43 yrs old, he's 46. I feel betrayed with no absolute proof. ???