Can I be reimbursed for expenses that I incurred while living at my ex-girlfriend’s palce?

You only have a case for reimbursement IF at the time you made these payments, they were made as a loan (or in the case of items you bought, you bought them for yourself, and merely happened to have them in the girlfriend's house for your joint use). If you can show that you either never gave items to your ex-girlfriend, or loaned money (including by making payments for repairs on her behalf) with an agreement (whether written or oral) that she would repay, you can recover the items or money.

On the other hand, if the payments or items were a gift when made--you paid the costs, loaned the money, bought the furniture, etc. with no expectation of repayment--then you cannot recover them; if something is a gift when made, the giver loses all claim to it and may not retroactively or after the fact try to recover it.

That's the law. As a practical matter, if your ex-girlfriend will not agree that these things were loans or were owned by you, but instead claims they were a gift, if you sue her, it will come down to who is more credible and/or has more evidence (like emails or text messages) on his or her side. Note that if you sue her--which you'll have to do if she does  not voluntarily repay--the advantage lies with her; as the plaintiff, or person suing, you have to prove your case by a preponderance of the evidence, or that it was "more likely than not" that these things were loans or belonging to you. You must be more persuasive than her--if everything is equal, she will win.