Better consult with an attorney.
If that guy is legally separated but not divorced, there are all kinds of situations that may not bode well for you, especially in a community state (married couples).
If you put him on the deed -- does that mean his wife can lay claim on the property too?
If you're taking out a loan, is he going to be on the loan application?
If he buys property as a married man, won't he need to get his wife to do a quit claim deed on that property?
How will you take title -- as joint tenants or tenants in common? If you pass away, entire property goes to him due to right of survivorship. So your heirs are left out. If you do joint tenants, your respective heirs get your respective parts of the property when either one of you passes away.
This is not the best place to get the answer to your dilemma. Get thee to a lawyer, post haste!