I have an urge to cheat on my boyfriend that cheated on me

I found out about two months ago that my boyfriend had been sexting other girls the whole time we were together (11 months at the time that I found out) we've been fighting about it since then and trying to hard to make our relationship work but it's been very difficult to work through it and I'm still in so much pain over this and I can't forgive or trust him but I'm trying so hard because I love him and i don't think I would ever find anyone else anyways I'm going to a party tonight and I know it's so wrong and so messed up but i have this urge to cheat on him too to kind of make it even I just mean a kiss or something and I wouldn't even tell him about it so I don't know why I feel the need to do this and I really don't even want to i just feel like it's not fair that he gets to hurt me and I know how immature and wrong this is why do I feel like this