If you are not happy break up and move on. Life is too short for shitty unfulfilling relationships.
Okay so I've dealt with anti depressants personally and with significant others and I don't want to give you bad news but most likely this isn't a good thing. First, if you really see this as a serious relationship that could have a future, you're going to want to give them time to adjust because starting and/or stopping anti-depressants can take a while to level out. The bad news though is that anti-depressants can numb you so much that you become complacent, in your life, job, and sadly even relationships. Sometimes when you get off of them and clarity starts to come they may have realized they weren't actually in love with you the way they thought they were.