Cases of 'being groomed as an omega' are incredibly rare, in my experience - like, I've heard of it happening between individuals, and my model supports a couple of cases where it could look like a group thing because the individual who's decided to do that has followers who will go along with them (aka bullying), but for the most part when it comes to social groups that aren't built entirely around a particular leader (which is usually fairly obvious), they're either broken enough to shit on most everybody in them to one degree or another, or cases of abuse are the unintended result of personality conflicts or fairly predictable responses by group members to the abused party's behavior. (This is only intended to cover cases of keeping someone around to have them be an omega, though - trying to drive an unwanted interloper out by making them uncomfortable also happens, and I think it's fairly common but I'm not sure of the frequency - how I select for groups to interact with biases me too much to comment on the issue.)

I suspect from your description of things that that last thing is the case for you - that you're making it easier for people to treat you poorly than to treat you well, which ends badly unless you're dealing with people who refuse to treat people poorly even in the face of that situation. If that's the case, it's a problem with a few different solutions; 'strongly select for people who refuse to abuse others' seems likely to be the most viable one for you in the short to medium term. (Possibly in the long term, too, though I suspect that if it works, you'll end up learning enough to be able to relax your selection criteria some.)