Trust can absolutely be regained in a relationship. I know from experience, I lost the trust and regained it back and it's now stronger then before.
I'm not saying it'll be easy but #1 You need to decide that you'll do whatever it takes.#2 You need to trust yourself first and by this I mean you need to know fully who you are and what you stand for and other people need to know what they can count on you for without you having to tell them. And #3 You need to be your word and by this I mean do what you say your gonna do. I'm an ex bodybuilder and now work as a relationship Coach, and so many guy's don't get this one. If you say something to your woman Do IT! Even if it seems small to you. Because women test their men to see if they can trust them or not. So BE YOUR WORD.