Should I return to what I'm familiar with or begin something new?

I'm a 22-year-old woman facing a bit of a dilemma, and since I'm still young, I’d really appreciate some unbiased advice due to my past mistakes. I have an ex, a 22-year-old man, with whom I’ve shared a lot. He made some mistakes, including breaking up with me once because of our long-distance relationship, but he returned when I began to move on and showed that he had changed. We ended up living together, but during those two years, I discovered that he and my best friend, a 23-year-old woman, were exchanging explicit messages. I’m unsure if anything physical happened between them, but despite his assurances that he had changed, I continued to find evidence of his disloyalty on his phone and through his actions. We ultimately broke up about six months ago. Since then, I’ve started to move forward and met a wonderful guy, a 27-year-old man. He’s very mature and seems to have his life together; we’ve been dating for a few months and have shared many experiences together. Now, my ex is trying to re-enter my life. He hasn’t directly expressed a desire to reconcile, but I sense it. We’ve had our fair share of bad times, but also some truly great moments, and he was my best friend. Letting go of that bond is challenging for me, despite the universe seemingly pushing us apart repeatedly. The new guy is fantastic, but I find myself feeling anxious about the uncertainty of something new. I'm torn between the connection I had with my ex and the potential for a brighter future with the new guy. What should I do?