As for the meaning, I think it's simple. The relationship he's in isn't ideal. It's a lot of struggle and pain on both sides. But he has another girl on the side, and when things go wrong with the first one, he runs to the second one for comfort. Of course, this doesn't have to be taken so literally. His "secret love" could easily mean some other form of escape, like his writing or something.
As for the meaning, I think it's simple. The relationship he's in isn't ideal. It's a lot of struggle and pain on both sides. But he has another girl on the side, and when things go wrong with the first one, he runs to the second one for comfort. Of course, this doesn't have to be taken so literally. His "secret love" could easily mean some other form of escape, like his writing or something.