I need advice on what to do next in my relationship?

hi im a man of 28 yrs old who has been living with my partner for the last 10 years we have three beautiful Gurls whom i adore and whould do anything for all of them, recently we have had some problems in our relationship relating to me taking advantage of her love by playing on my xbox till the early hours off the morning and obviously get up much later in the day than i should have and possibly not pulling my weight enough with the kids she had told me what was going on but the timing was poor on her part as she told me wen we were argueing and i thought she didnt mean it till the day i saw it in her eyes that second my world started crumbling and i realised what i had done and instantly realised i had messed up big time and what i had too lose which was everything as i love her and the kids soooooo MUCH she asked me to marry her about a yr ago i said no because i was scarred and now realise this was the biggest mistake of my life as i would marry her in a millasecond know so having spoken about the situation we decided to give it another go i felt like a 100 million ton weight had been lifted off my head and things were good i pulled my weight got up i was never on my xbox and things looked rosy till i found a message on her phone from my BEST MATE this happened as i had agreed to letting my girlfriend recieve driving lessons of this guy as i trusted them both implicitley but things turned weird and i felt it a couple of months on when he no longer came to see me also trying to keep my friends away from me (he was the driver) asking weird questions about a friend who likes a girl at work he likes. alarm bells started ringing but i had NO evidence and i told him no probs unless you are breaking up a family just incase he was talking about me so i carried on without knowing till i saw the messages after a outing with my mates wen i asked another mate how much it was to get married and he started acting weird again so i checked my girls phone to make sure he was being normal and he was not there was kinda weird messages were he was trying to see if it was alright to msg sexual type messages and also a message saying xxx i want you soooo bad xxxx which tore me apart i went mad nearlly stormed round his and smashed him in my girlfriend didnt tell me as she was protecting me from lossing all my friends and was gonna tell him to back off the very next day but know she says she dosent know if she wants to be with me any more im just hanging on not knowing my future im in pieces and need my girlfriend and kids as they are my life any advise would be appresiated as i dont know what to do i try to be normal but its sooo hard please dont be harsh im hurting badddddd many thanks xxxx