AITA for getting back with my cheating ex

Hello! I (25F) need advice for whether or not to get back together my ex (25M). My ex and I dated for 6 years and have been broken up for 4 years. Our relationship towards the end was not great and he eventually ended up sleeping with someone else. This obviously ruined the relationship and I broke up with him. He has been very apologetic and has tried to fix things over the years we’ve been apart but I’ve always denied him. But 4 years later and we can’t seem to leave each other alone. We have been talking and trying to figure out where to go from here. He wants to get back together and has made it very obvious he’s still in love with me. He has put a lot of effort in to making it sure that things will not end like it did last time. Obviously I have reservations and I’m not sure if the past should be left in the past or if we should try again. Please help.