DOMA was the least bad option that we had at the time. Had the GOP wanted to get a Constitutional Amendment passed, they would have. They would have had the votes.
Again, though, marriage equality is not the end all be all of everything. If I held it against every single person who was at one point on the wrong side of the issue (as Bernie was, as he supported unions more than marriage), there would be about six people in the world I could consider voting for. All I care about is they are on the right side now.
When I look at policies that have made an actual effect on LGBT people, Hillary's done a hell of a lot more in her role at State, let alone on visibility issues to the community. I do not trust Bernie on this issue. I simply do not. He has yet to prove that he understands how our community is impacted outside of income inequality, which is not as powerful an issue among gays and lesbians. (Our trans brothers and sisters suffer from income inequality at far greater levels than queer people do, though. I will give him that.)