Wow! I can imagine that being pretty darn disturbing! Let me start by pointing out, as I've done before ;P, that what might seem extreme and tabboo in our waking conscious is typically not at all about the literal imagery (sex is only ever about sex when the dream is a wet one, and violence is never about physical violence).

My first instinct was to respond with how cutting yourself open is a need to have someone see the inner you, the -real- you. But then you said "into little bits", and now I'm thinking "what purpose would being diced up serve symbollically?" It could be that you want him to see the different PARTS of yourself, and how they are separate from eachother. It could be that you want him to know every bit of you personally (using a chainsaw is a VERY personal attack), and I don't mean that sexually. The scattering of your bits into a lake has two distinct symbolisms for me. First is the occurence of water. Water is usually a symbol for the emotional/spiritual realm,depending on the context. Actually, usually it's either emotional or both at the same time... The othe symbolism is death (think scattering ashes). Death psychically/emotionally/spiritually is NEVER just about something ending. In the mind, as with in the universe, things happen in cycles. The death of one self allows for the resurrection of a new self - a more developed and whole self. That you required the ex to cut you into pieces, not just scatter your bits, tells me that what was keeping you from continuing the cycle was somethign regarding the relationship. And that the dream still haunts you tells me that it's still relevant in your subconscious. You haven't been able to complete the cycle and grow.

Ask yourself these questions ::
- What about the relationship with your ex was stifling to you personally?
- What about you form DURING the relationship were you not pleased with, and what of those has not changed?
- How would your ex have been helpful in overcoming these flaws, and how was he preventing that help from happening?
- How can you overcome these flaws on your own?

I think if you answered these questions, you might be on the path to resolving this lingering dream.