Here we go again, Heidi's a Gemini and Seal is a Pisces. These two signs are 90 degrees, three houses apart, on the astrological wheel. Therefore the energy is square which is negative. I don't know what brought these two people together, but it wasn't for the right reasons. There was an ulterior motive.
A Gemini dealing with a Pisces is a mind-oriented person dealing with a ball of sensitivity. It doesn't get further apart than this. She was always tap dancing around trying to not step on his feelings. Seal has a Grand Square making all the planets involved focal planets -- Sun (narcissistic tendencies), Mercury (not male or female and tends to lend an air of coldness), Moon (overly sensitive), Saturn (ambition), Pluto (very invested in right and wrong). Too many focal planets and you have too many balls in the air all the time. You're difficult to be around. He also has, as one of my readers pointed out, a Mars/Pluto square. You can call that rage. And with all the traveling they both do, it's a miracle they stayed together this long.
Seal has predictive Mercury (communication) square predictive Saturn so his power has been blocked in a big, get-over-yourself way. Heidi has predictive Venus (love) opposing Jupiter (excess, the law) saying, "I'm walking away from the thing that you do too much."
When these relationships, that should never have been relationships, fall apart, they won't get back together again.