Yes, he can sue you. But the question is will he prevail? The answer there is twofold. On the one hand, lawsuits can be expensive. He and you will have to decide whether either can afford to pay an attorney. Disregard the common notion that you can find an attorney cheap who is willing to take a percentage of the sum collected. He might but I'd be surprised. You would have to pay your attorney to defend you. Now, secondly, and more to the point of the substantive aspect of suing you. First, I assume the remodeling improved the garage. Second, how much, to what degree. Third, is did you both have an agreement as to who paid the materials, the use, etc. That very easily could limit the amount he might be able to prove. You might consider a mediation service prior to his filing a lawsuit. But at this time, it appears that he is angry because of the personal break-up and he might consider a small settlement just to get him out of your hair. As always, you should consider retaining an attorney to negotiate on your behalf. Good luck.
Answer Applies to: Oklahoma
Unless there was an agreement to pay him the answer is no. He can sue you but will not win.
Answer Applies to: Michigan
The short answer is that he can sue you, but his likelihood of success are somewhat slim. Assuming that the two of you do not have a written agreement that states that if he puts the money into the garage, he will get something in return, typically an ownership interest, all your ex has to rely on is the theory that an oral contract was entered into between the two of you. Your ex would argue that he put the money in with an understanding that he would get something back.
Answer Applies to: Michigan
Anybody can sue anyone for anything at any time. We live in a litigious society. That doesn't mean however, that if your boyfriend is determined to sue you he will win his lawsuit. The money your boyfriend spent in remodeling your garage sounds like a gift. Once you boyfriend gives you a gift he has no rights to the gift and cannot take it back in the future now that you broke up. The issue becomes then is whether there is evidence to support whether the remolding work was a gift or whether there is evidence to suggest you were going to compensate him for the work. This situation would be different if when your boyfriend remodeled the garage you agree to repay him for the money he spent or agreed to compensate him for his labor in remodeling the garage.
Answer Applies to: Massachusetts
While he can sue, he will not prevail. He can claim that he used hi own money for the remodeling, he paid no rent. If he was on his own, he would have. Thus, he earned a benefit, which he paid for by the remodeling.
Answer Applies to: Washington