My inadequate boyfriend's constantly whining. Tempted to cheat again.

I've been seeing my current boyfriend Davie for about 10 months now. We started off great, he wasn't my type at first but I gave him a chance. I'm a good looking man; 6 foot 2 with a nice body. I work out 4-5 days a week and catch guys checking me out on a constant basis. What can I say? I live near San Francisco where there's plenty of gay fish in the sea. Meanwhile my boyfriend Davie's only 5 foot 1 which was an immediate red flag, but he's Spanish with long hair and a beautiful face and was nice at the time so I just said fuck it. Things seemed great at first... he was funny and I even grew attracted to his thin small body; until 2 weeks into the relationship when we got into bed. He's a great kisser and all, but when he took off his pants... wham. Smallest dick I've ever seen. I asked him the size since I was in shock and he said he was 5" and that it was average. I myself have a penis that's 9" or so and have never seen anyone his size; so I did my research. Turns out 6" is the average and he had lied to me; which was another red flag. To make matters worse, I measured it one night on his sleep and it was only 4.5! I was so shocked but figured I'd give him another chance since I was already in it. As time went on he started opening up about his past and how he's been cheated on. He says I'm the only one who's stayed with him this long. He's a great guy on the inside, buys me flowers and makes me my favorite things to eat, and he always tells me how much he loves me. We cuddle all the time which is nice; but at the same time feels like I'm hugging a small child with body hair, which makes me sick. Regardless things were great until he caught me cheating with my co worker. He cried, made a scene and left to stay with his parents for a week. I called him and apologized, and at the time I did feel kind of bad. He forgave me and moved back in after I promised I'd never cheat again... but as time goes on it seems like I'll end up breaking that promise sooner or later. He's been more insecure and emotional than ever before. He's gained weight, is really depressed and is always sad, and he constantly needs my reassurance. I tried to help by buying him a gym membership since he's gained weight but he cried about that too. Each night now he cries in my arms and tells me I deserve better, which only makes it more tempting. I don't want to cheat again because I'm the best thing he could ever ask for, but its hard when there's so much wrong with him. He's the perfect boyfriend on the inside. But how can he make up for his height, dick, insecurities and now his weight? If he had one of those problems I could work with it but all 4 is a joke. It's so tempting with valentines day just around the corner to cheat when all I have to look forward to is some candles, maybe a rose or two and boring sex. I just don't want him to hurt himself if I break things off so I don't know what to do. Should I dump him? Is he worth it when there are so many other men out there? Let's be real; I'm a young 25 year old hunk, why should I have to settle this early on in life? It's only realistic. Advice?