Trust is a big issue in BDSM and that is a barrier to online relationships (whether you end up meeting for real or not). And yes, there are many out there who are dangerous or just pretenders and male Masters for female subs is an especially dangerous ground to tread for someone who is not aware of the dangers.
The trick to secrecy is finding someone who has a similar level of desire for privacy. Some lifestylers are 'out and proud', others are more discrete. I would suggest if you were really serious about finding a real time bf who is a Dom looking into your local BDSM scene and finding a munch.
A munch is a vanilla meeting of BDSM lifestylers and usually has rules which must be followed. Usually these rules include:
- A discrete but public meeting place. A pub, restaurant, cafe etc. You have your own table for your munch but there may be others around who are not kinky.
- A dress code which includes NO kinky or fetish wear. A leather jacket or boots is fine but a PVC catsuit or gimp mask is not. Common sense usually applies - anything which draws attention to the group as being 'kinky' should not be worn.
- No playing. You can talk about the lifestyle, you can make arrangements to play at a later date in a private location but you should never do anything that draws attention. So, a sub buying a drink for a Dom/me and serving it to them is sort of ok but no kneeling or punishment or anything like that.
Basically the idea is that you are just a bunch of friends having a meet up for drinks or dinner. Nothing unusual about that at all. You talk about stuff - kinky stuff if you like but conversations could also go into vanilla topics. You get to know everyone. Because this is a public place, you can get to know someone quite well without having to meet them alone and risk the dangers.
Most lifestylers are as equally reticent about revealing their kinks to the world. The majority only really ever go to the extent of wearing a collar in public and there are enough women who wear collars who are not kinky to make that unremarkable.