Should i seriously feel guilty?

My ex girlfriend (lets just say her name is Jen) that lasted about 6 months recently found out i kissed my ex from a year ago (lets say her name is Tiffany). Jen and I broke up about 3-4 weeks ago, mainly because she lied too much and she broke up with me for another guy who she admittedly said "she thought the gr was greener on the otherside". I felt kinda lonely and i kissed Tiffany 2 days ago, and she found out and started saying i was s im an absolute peice of shi*, that im worthless, useless, pathetic and the most repugnant thing shes ever met... I uh.. i know shes probably hurt but, after being left for another guy, i knew where i stood, and i felt really lonely and really close to her at the moment, thats why i kissed her. Should i really feel guilty..?