Should I try to get with someone who I wrongly thought was single
Are you worried about her partner finding out?
No. I like the danger of it all.
If someone is in a relationship already, it is not a good idea to get involved with them. Their partner will come after you when they find out.
I'm going ahead with it, I don't care.
I really don't think you should continue going after this person. Even if you don't care about the trouble it could cause for you, you should be concerned with the trouble you could cause for her. I'm sure you could find a single woman if you just keep looking.