Look, he was never good enough for Padme. Jar Jar Binks was more his speed.
People talk about Anakin, but they really don't know him. I went to Jabba the Pizza Hutt with Anakin, and let me tell you - he is one cheap S.O.B.
Anakin had his chances, but he blew them.
Several factors lead to the Republic's fall. The major one is Palpatine's manipulation of the galaxy and the Senate. By creating a war and controlling both sides, even if the Confederacy of Independent Systems won the war, which they ended up losing anyhow, he would still be in power by controlling the CIS.
Also, the Republic could not have lasted anyways. Corruption and the Senate's inability to solve disputes, as indicated by the Naboo crisis, could have ended the Republic's functionality as a state.
Palpatine just used him. The chancellor craved power, even aroused by it. He introduced Anakin to the dark side, and convinced him to join it, using Padme as bait. Think about this: Your mother just died, your masters appear to hate you and not trust you, your wife is pregnant, you're not even allowed to have a wife or children, and you want to protect her. Sheev tells you that you can bring her back if you join him. Wouldn't you?
The republic would has fallen anyway even without anakin skywalker.Palpatine is to blame and he is truly evil who are main causes all the evilness that has brought to the galaxy.Anakin wouldn't turn into darkside if it's not because of palpatine.Palpatine manipulate anakin so that he could have power to rule the galaxy.