I'm 99% sure my significant other is cheating, but I don't have the money to leave.?

The house we live in is his, but we have a contract saying I can stay here for 5 years because I put the down payment on the house. The contract is notarized. There are lots of details in the contract stating that he legally has to help support me in a place of my own if the relationship goes belly up. I am handicapped and working is difficult.

I'm trying to get prooof that he is cheating but he is EXTREMELY careful and discreet. There are many reasons why I'm am almost positive this is going on... not just assumption or jealousy. Anyone know of a sure fire way to prove it? I could then get a lawyer and get out of this stressful situation. And no, he would never admit it unless caught. All I want to do is move on, but he still owes me 2 1/2 more years. Says he can't afford for me to live elsewhere, but he has over $20,000 of credit and at least $1500 leftover after bills paid.