How much equity does person have in a house, if he's on deed & loan with another but hasn't paid in over 6 years. Is it still 50/50?

My wife purchased a house in Sept 2008 with her then bf. 5 months later they break up bitterly. Break up is mutual after he cheated on her. He verbally agreed to give up his portion of house in return to not paying anymore for it, as well as not paying her grandfather back the $15k loan for the downpayment. In return she was to refinance under her name alone when she qualified by herself. She has not been able to qualify as of yet. They are both on deed as joint tenants with right of survivorship and both on the mortgage loan. He just contacted her last week after 6 yrs & now wants to be bought out of the house, to buy her out, or to sell house and split profit. House has approx $100k in equity currently. He has not paid one dime in over 6 years. She has kept up the taxes, insurance, home improvement and mortgage payments by herself. Is he still entitled to 50/50 even though he abandoned his half & reneged on agreement? We currently live in the house, can we be forced to sell?