Bret Michaels has called off his engagement to Kristi Gibson after an 18-year relationship.

Poison front man and reality star Bret Michaels has called off his engagement from Kristi Gibson after proposing to her nearly two years ago in 2010 on "Bret Michaels: Life As I Know It." The couple is hoping for an amicable split.

"Although the couple have separated they remain great friends and are committed to jointly raising their two daughters," Michaels' representative told People on Monday.

Michaels and Gibson have two children together, Rain, 12, and Jorja, 7, but the "Celebrity Apprentice" winners have remained apprehensive about marriage for years.

"Love and marriage are the ultimate," Michaels told People before he popped the question in 2010, "but I still get a little sweaty about the marriage thing."

Altogether, the couple has remained together on and off for about 18 years, according to Michaels' representative.

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Studies have revealed that cohabitation can often lead to such problems within a relationship because often, couples move in together for very different reasons.

"Women tend to agree to live together because they think it will lead to marriage. But they still want a man to propose, to put a ring on their finger, to say: 'I will protect and look after you,'" clinical psychologist Dr. Helen Nightingale told Daily Mail. "For men, however, cohabitation may be a way of actually putting off commitment because they're not sure they actually want it."

In addition, once a previously cohabitating couple does become married, they are more likely to get divorced, research suggests. Based on a 2002 study by the National Center for Health Statistics, 28 percent of couples cohabitated together, 7 percent of those never tied the knot.

A second study in the Journal of Family Psychology revealed that 12 percent of couples became divorced after living together first in comparison to 11 percent of couples who were engaged before living together, and 10 percent who never lived together at all.

"We think that some couples who move in together without a clear commitment to marriage may wind up sliding into marriage just because they're already cohabiting," lead researcher Galena Rhoades of the University of Denver explained.

Higher levels of dissatisfaction were also reported in addition to the fact that a higher number of unplanned pregnancies were reported among those who cohabitate.