Getting involved with somebody if they are separated...

I would like some feedback, advice, or suggestions on whether it is okay to become involved with somebody who has been separated from their spouse for 2 years now. I feel like in my heart, I already know the answer to this, and that would be to not get involved with them until they are divorced, and quite possibly then not even for a while. Does anybody know of any Bible verses that would support not getting involved with somebody while separated? Doesn't it mean that legally they are still married even if they are separated? I have talked this over with a couple of people, one person asked if there was such a thing as 'legal'separation, another person has said that this person is not going to get back with their spouse. I guess my reasoning is if it has been 2 years, isn't that long enough to know whether or not they want to stay married, & also, can somebody give their whole heart to another relationship if they are still married, even though separated? Also, would this be looked upon as committing adultery, on the part of the person who is still separated? And I'm not sure what it would be looked upon on my part, I'm not in a relationship, but I am am aware that this person is separated, it's not like I don't know. So knowingly getting involved with this in mind, what would that be considered?