I always think of the verse in 1 Corinthians that says, "Love always trusts". However, I also realize that's easier said than done and it doesn't mean that we allow someone to take advantage of us time and time again.
I know this feeling all too well, Ethie. Trusting used to come so easily to me and I never had any trouble with it at all. Over the years I began to notice that people took me for granted and would abuse that trust, doing whatever they wanted and always knowing that they could come back to me again and I would just shrug it off. It took someone breaking my heart and making me look and feel like a total fool before I realized just how far my trust can go. I forgave and moved on but the memory and fear of that event still haunts me, only because I'm terrified of it happening again.
That event, coupled with something work-related at the time, left me shattered and has made me a nervous and paranoid person. I've never been a suspicious person but after that time trusting is so difficult for me and I feel like I'm walking on eggshells every day, just praying that people are who they say they are and that they genuinely care about me. I'm getting better and God has healed some parts of that. I'll admit that I still have a way to go.
I believe in second chances and if it's someone you love enough then I believe anything is possible and God can reconcile that divide. It takes two to make that work, though. If the other person isn't willing to change or prove they're trustworthy then there isn't a whole lot you can do. It's also made me even more committed to be a trustworthy person. I know how much it hurts when someone breaks my trust and that only motivates me to be as honest and diligent as I can. I'm who I say I am and I do what I say I will do. My word is very important to me and in my relationships, especially my romantic one, I want there to be no doubt that I can be trusted and believed in every area of my life.
Sorry. That was probably really unhelpful. I'll be praying for you.