I need different perspectives please!

In June my boyfriend and I were laying in bed one night and I knew something was wrong so I asked him what was on his mind and he said he hasn’t been happy and he wasn’t in love with me anymore but he still loves me. I asked him if there was someone else and he said no, so I told him let’s take some time apart maybe he needed his own space so he moved back in with his parents and I’m home with our daughter (who was 3 months old at the time) a couple days later someone he works with sends me an anonymous message saying they suspect he’s messing around with another coworker that they’ve been eating lunch together a lot recently so when he comes over I asked him about it and he says they get lunch and that he does indeed like her. For so long I questioned why he would do this after I just had his baby, why I wasn’t enough or pretty enough, I’ve done so much for him. He says it was never physical but he did have feelings for her. I know I sound pathetic, but I so desperately want him back because I love him, I’ve never stopped loving him and he’s my best friend, deep down I know he’s my soulmate and we’ve been together for 4 1/2 years. He was always such an amazing person to me, I just don’t know how to get through this anymore. I told him I had to let him go because if we were meant to be he’d come back but nights are so hard, I stay up at night wondering where things went so wrong. I miss him all the time, I just don’t know how this gets easier. We still go to dinner together, do couple things together sometimes but we aren’t dating and I know he loves me, he tells me he loves and misses me so I just don’t understand why he doesn’t come back? I need insight from anyone who’s been in his shoes, who might understand why he’s doing this?