Ask your lawyer. If there is no "cohabitation" language or marriage clause, you likely won't lose the contractual alimony. But talk t your lawyer.. You hired him or her.
I am not intending this to be legal advice, because I don't know the particulars of your situation. Call me if you would like to discuss this or other isues.
I agree with Attorney Moore.
However, be advised that if the boyfriend moves in that the ex might claim you are "common law" married. You probably want to talk to your attorney about Texas common law marriage rules.
You might not want to move in with anyone of the opposite sex if $2,500/month is worth it. You risk losing it or having to go to court to fight to force him to pay you. For example, one husband stopped paying in exactly the situation you describe. Wife is now having to sue ex for her spousal support & incurring thousands in legal fees to collect the money she claims he owes her. He claims that the co-habitation voids their agreement. Moral of story: Save several thousand dollars to re-hire your attorney if ex decides to stop making alimony payments when he finds out you moved in with bf.