I feel terrible for kissing a crush right after breaking up. :(?

i broke up with my first boyfriend 2 nights ago after 3 months. part of the reason is because i really liked this other guy. i feel so terrible now because last night that other guy kissed me. my boyfriend really really liked me and i probably only really liked him because of that fact, which saddens me. Anyway, i know that he would be really hurt if he found out about this other guy. he already was jealous of this guy cause he was convinced me liked each other. i cant stop thinking of ways to punish myself for kissing the guy back last night just a day after i broke up.