Is it even worth it?

Anyone ever considered getting back together years later? Ive been broken up with my daughters dad for about 3 years and a half, and about a year or so after the breakup I thought about getting back together. I noticed he was on his phone a lot more and come to find out he had been talking to another girl. He claimed there was never any sex or anything like that. Things didnt work and years go by. Recently I started seeing my daughters dad again and began to even have sex with him. Things had been a little rocky because he claimed to work a lot and never had time to come see us. We decided to take a trip together. Deep down in my heart I knew something was off but he just told me I was being crazy and that he had changed. Well I decided to go through his phone and low and behold he had been seeing the same girl from the first time we were trying to work things out. There was all these messages including the sweet names and the texts after hanging out including times he was supposed to be working. Once again he claimed they hadnt slept together but my rage got the best of me and I texted her asking if she has been sleeping with him because I have to. She said they hadnt had sex in years but that confirmed that he had lied to me previously and that they had in fact had sex the first time I suspected it. Im just so hurt and I cant imagine being able to forgive him and move past this. I feel like an idiot for believing him