I have ended a 6 yr gay relationship, can my ex sue me for 30,000.00 she says she put into our joint acct. that we used jointly?

The answer is not if your Ex can sue you, because anyone can file a suit, the questions becomes can she prevail. In order to file a suit the "plaintiff" in this case your ex, needs to decide under what type of action does she have a claim.

What this means is that she needs to claim that you broke some kind of an agreement or duty to her. That this "breach" of the agreement or duty caused her some kind of loss, and that that loss caused her damages.

In the scenario you posted, it will most likely be hard for her to prove to a court that she had a resonable belief that you would not use money she put into a joint account. But without significantly more information, I cannot give you a definite response or defense.

First, you need to determine what she is actually claiming, then you would need to look at the rules/laws to see if she can prove the damages she is claiming.