My partner of 6 years has a history of lying to me. He was raised to believe that any way you could get out of conflict, get out. That included lying. He has admitted to me that he has lied most his life. Not all the time big things, sometimes little things - but lying nonetheless. Vicious cycle.
Over the course of our relationship he has lied to me about women many times. This, obviously, has created a lot of problems and trust issues over the years. It got the the point that I would have evidence (emails, texts, etc) and would be showing them to him and he would still try got get out of it, regardless that the evidence was in my hand. We just had another incident a little over a month ago that just almost did it for me, i.e. I thought I should end the relationship. I am a VERY open, honest person. I do not judge, and I always encourage honesty. Not getting that honesty, for me (& probably anyone) can be very tough and hurtful, as well as confusing & frustrating.
When I get those "what if he's lying.." thoughts, I have to remind myself that A. I stayed in this relationship. What I mean is, I have to work through these feelings because I made the decision to stay and work through them. I could have just left the relationship and moved on but I didn't. I stayed & made the decision to move on and trust him so I have to figure out ways to turn off the negative thoughts. B. For the most part I HAVE to tell myself "OK. You have to trust him. You have to. Give him the benefit of the doubt until you have 100% reason not to", i.e. evidence. I do not snoop, I do not ask 37462 questions or check texts or emails or anything of that nature. I think that only breeds mistrust because you are trying so hard to find something that you're only creating a bigger problem. There has to be a point where you start trusting again.
That being said, it takes two to make this work. He has to be willing to calm you and make sure you know what is going on. He needs to be able to confront your fears and make you feel better about them. By no means do I mean berating him with questions or accusations, but if you are feeling a little insecure I think its good to voice it and work through it together. Letting things fester never solves anything and only breeds resentment and anger.
I know what you are going through. Its real tough. It takes a strong person to remain in a relationship where trust has been shattered numerous times. However, you are still in it & if you work at it you will reach that point where you say "OK, were in a good place. I feel secure - Im letting this argument go and moving on". Im not big on "if its meant to be, it will" because I really feel like everything in a relationship (or relationships) requires work. Keep it open and honest, communicate as much as possible without being suffocating and you will move forward. Good luck.