A couple good questions have been raised that we need to know the true answers to before we can give solid advice. When I say true answers, I mean her intent, not some BS she will feed you.
1.) Does she still live with him? If so, they arent separated.
2.) Why has she been separated for 5 years? If she still lives with him, this question is dead because she isnt really separated.
Let me tell you about a chick that I was seeing for 6 months from the beginning of 2018 to June 2018:
She has a doctorate degree (medical field) and her husband (now ex husband) is an attorney. They were separated for 5 months (as in not living together) before Glassguy slipped in. The now ex husband told her that he would do the dissolution paperwork and get it done. This little game went on for 3 months and he never did a thing. Meanwhile, he strategically balanced his income down so that when she would hire an attorney to file (and she eventually did---with my attorney) he wanted her to pay him alimony. To the tune of $3k a month. They had 2 dogs and no kids. Married 14 years.
So the first few months she would just come over and fvck. No problem.
As she started developing feelings, she wanted to see more of me. The problem is that I like to go out and do fun stuff. I am not the sit at home type on the weekends. So she didnt really want to go out because she didnt want people to see her with someone who didnt know that she was separated. That was an issue, so I tried turning her into plate status and fwb only and no dates. Then she got mad because I started seeing other people.
The soon to be ex had emotional and financial leverage on her. Glassguy doesnt make a good emotional tampon so this became a problem really quick.
So I was dealing with an emotional up and down mess, she wanted me to sit around my house with her all weekend and didnt understand why we couldnt have a "real relationship". Like wtf?
I saw her this past New Year's Eve. She was with a female friend of hers at a big DJ Dance party. She drank with my group and danced on me all night. She kept telling me that she had plans to "marry me". She didnt take kindly to me inviting both her friend (who is cute and was all over me anytime the chick I dated previously went to fetch drinks for us) over to my house for a night cap threesome lol.
Dating a married woman, separated or not, is never worth it. Granted its fun in the beginning because of the taboo, but shyte can go south really quick and you will find yourself dealing with an emotional tornado.
One cannot be in a relationship while still in another.