The only time God's forgiveness has a limit is when one does not repent. When one does not seek forgiveness, they cannot be forgiven.
Saying that, one must also realize that when one repents without repenting (in other words, just says they're sorry to keep themselves from hell, fully intending to sin again in the same way), that is the same as crucifying Christ over and over and over again. We all struggle with sins and addictions and anyone that pompously says they do not are lying. When we are set free from a bondage, we notice another one that must be dealt with. As others said, we can do all things through Christ who strengthens us.
I had a sin that was destroying me. I wanted so desperately to be free. Yet, apparently, I wanted it on my terms. Therefore, I remained bound, lost, and miserable. One day, after I'd committed the same sin again, I fell on my face on the floor and cried out, with tears streaming down my face, "I'm so sorry, God!" Immediately, I felt peace. It was so forceful that I actually stopped crying and looked up and around. Foreign and strange, the weight of shame and despair rose from me. I decided that couldn't be "right", so I began crying out to God again. "I already forgave you," He said, "You asked and I've forgiven you. Now, get up and move on." He showed me that day that the beating myself up when I'm genuinely repenting was a form of self-abuse so that I would feel like I repented enough to be forgiven. One doesn't need to beg God to forgive them. They just need to repent.
Later, after giving into this sin again, I was listening to the song While I'm Waiting and I realized that I wanted to wait on God and serve Him without being in the bondage to that sin anymore. At that point, I realized that I wanted God and a relationship with Him without the sinful acts I'd been committing. I wanted Him MORE than the sin. That was the day that I was fully set free.
There will come a day when you will chose to be set free according to His terms, rather than your own. You will choose to surrender fully to Him and the sinful things of this world will lose their power. You will want Him more than the bondage you've clung to for so long. It's beautiful when that happens.
Now, I'm free from that bondage, yet I still have other sins that I now have to deal with. Mainly, my attitudes. But, each day, with grace, mercy, and love, I face the sins of attitude and I seek to be more and more like Christ.