I have been with my boyfriend for a year now , a few months ago he meet someone at work they talked but nothing happened apparently she gave him her number and he called her , when he did , he told me right away he said he was sorry and gave me her number to call her , I did she said nothing happened and the conversation ended there.

From there on our relationship went downhill I never forgive him about that and since we both work in the same place , I knew she was still around and couldn't even concentrate in my work knowing they were both in the same area of work . I keep fighting everyday and our relationship got strained I started to notice that he started to change towards me he got cold and distant the reason? He said my fights were too much .

One day I was walking with him at work and she was right in front of me , I then took the opportunity and said to him: ask her if you and her are together right in front of me . He said to her :tell her that we are not dating , to wich she reply: we are not , but he keeps talking to me specially on sundays that we work together , he is trash and I don't want anything to do with him , I ask him : is she correct about this? He said :NO she is a liar , she said that she had witnesess . After that I stayed with him but doubted even more , we got separated for a week. We got back and she saw us together , but I think that he still likes her . I am 5 years his senior and I feel ashamed going through this things . I can't trust him , he has even said that before he dated me , he was a cheater in all of his relationships . I know I fight a lot but I simply don't trust him , what can I do?

You are paranoid. If he already said he is not cheating, then you are the one at loss.

Look if you have no evidence that he is actually cheting on you... then probably nothing is. Try relaxing... things will calm down... but if he did say he has been a cheater then usually cheaters don't change... try and relax though... take your time...

I can tell you that if you keep acting the way you're acting, you'll solve this situation yourself. He's already warned you once.

Being needy, insecure, controlling of his behaviors and accusatory... yeah, guys LOVE this stuff... NOT. He will end it himself soon if you don't snap out of it.

What can you do? Stop putting him on the defensive. Your fears are not an issue HE has to deal with, you have to deal with them.

You can admit your lack of trust, whoever you want to blame it on, and break it off to give you both some peace
You can stay, shelve the needy, aggressiveness and keep plugging away with him
If you go with "stay", you have to be nice. If you must come down on his head, at least wait until he ACTUALLY does something wrong, I mean ACTUALLY, not something that has to do with your feelings, something that has to do with his actions.

Don't worry, he promised you at the start he would cheat, just be patient.

Jealousy is a very dangerous thing that could cost you a lot. It's a race against yourself and you won't win without getting help. I know first hand what jealousy can do to a relationship. You need to trust him or the relationship is doomed. Pick one right now, stay and trust or get out.

That is very true... I had jealousy issues before as well... honestly it killed the relationship... (not completely but it for sure didn't help) You need to learn from this. If you think that the worst is going to happen chances are... it's going too. You need to just relax.

If someone told you that more is going on... then that's OK... take it step by step. But the problem is if the person you are with is not happy they will leave you even faster!

I agree with your BF.. your fights are too much!. If you have decided to be with him, you got to trust him... If you can't trust him let him go... I'm sure your head wants to explode.. This is not healthy... It's normal to be jealous sometimes, but above all you got to trust your partner... Like I said: if you can't trust him, get out... & if you decide to be with him, leave the other girl in the past.. He already told you nothing happened... By acting like this you're pushing him away!.

Having insecurites is not go my boyfriend had them and I found myself proving myself to him as if I was presenting my case in courtroom. Have guy/s treating you wrong in the past because that was the reason my ex was that way because the girl before me cheated on him and I paid the price, well our relationship did.

he has even said that before he dated me , he was a cheater in all of his relationships .
Nothing like fair warning.

I know I fight a lot but I simply don't trust him
Your not supposed to, he said he always cheats so in all honesty, he is a man of his word, what you didn't believe him??

what can I do?
Remove yourself from the situation, and get some help why you got involved with him in the first place.