Help with fiance...leave him or not???

Im not sure what to do and I dont know whether im paranoid or if there is truth in it but I think my fiance has cheated or will do and leave me. The night we got engaged he was texting his ex about meeting up for a shagg and he cant deny it because I read the texts but he said they were meant to make her jealous, he then bragged about the fact he could have another one of his ex’s back because she wanted him back, but the way he said it made it seem like he was happy about it. He also had pictures of girls on his laptop that are off msn, I had to delete an entire folder of semi-naked and fully naked pictures of girls off his phone. He has also privately messaged girls saying their fit and offered to send revealing pictures of himself to a few lasses, this is whilst im really ill in hospital, terrified all on my own! He lies about talking to certain girls and I just dont think I can trust him anymore, its to the point that I cant let him leave the house without being convinced he’s meeting someone else. Everyone says im insecure and paranoid but he has given me all these reasons and more to not trust him…I dont have the strength to walk away but I have no idea what to do anymore, its tearing me apart :( help!!!