Cheating partner??

So I have been with my boyfriend for 9.5 years. We have had a few problems ( as do everyone. A year or so in I went down his phone (whilst on holiday) to find out he had text an old friend he loved her. Of course I questioned him but he said it was an old school friend. We got over it. A couple of years later - I receive a message on facebook from a girl asking if was my bf. She had said he had been messaging her and said to go 'shopping together' he said it was a stupid mistake they hadn't met and yet again we carried on. Now the beginning of this year - after a blazing row I yet again went down his phone ( I know I shouldnt) to find that he had message one of his ex colleagues how beautiful she was in a picture which I find a little strange because If the tables were turned he wouldn't he happy. This weekend me and the bf were out for drinks for a friend's bday. I later in the weekend received distressed messages from my friend saying a friend of hers had seen my bf kisses some girl a few months back.

His adamant he didn't do this and is trying everything to get back in my good books. He can't believe I trust the friends comment over him. Now I just don't no what to do. Do I finish it? I have not evidence he did kiss this girl only words.

I'm heart broken - sorry for the waffle x