Hi, I'd like to help you with your question.
I can understand your concern. You do not want your daughter making a wrong choice in her life then either getting hurt or regretting her decision.
In this situation, time may be a deciding factor on how it turns out. You said your daughter met this boy when she was 14, which is a very young age. Although she is still with him now that she is 16, she is still very young. Given that she has two more years until she turns 18, there is a lot that can happen before then. Also, her boyfriend will have had two years of sitting around collecting unemployment. He may either grow up a bit and start progressing in his life, or he will still be sitting there, unproductive. If he hasn't progressed, your daughter may start to tire of dealing with this and move away from the relationship.
You can, of course, forbid her to see him. But this may end up backfiring on you. What you have done so far is good- you let your daughter know about your concern and have been open and honest with her. She is at the age where she is going to have to be responsible for making choices, and the mistakes that go with them, on her own. Otherwise, she will not learn how to avoid them when she is no longer with you.
Keep talking with your daughter. But do it in a way where you remain low key. By that I mean tell her you are worried but that you trust her. Tell her that you are there for her, no matter what. Let her know that you want the best for her and that includes a promising future. Ask her what her plans are for her future. Let her talk it out without judgment. If she works her plans around her boyfriend, as her more details about how she plans to do that. But don't show displeasure. The idea here is to have her see that although it all looks good in her mind, reality is different.
If she has a career in mind, help her explore it more. Take her to shadow someone in her chosen field of study or visit colleges with her. Do activities with her that are about her future. If she brings up her boyfriend, let her talk about it but don't comment. Try to remain as neutral as possible. That way, you do not become the enemy in her mind but instead someone she can turn to. If things with her boyfriend would become bad, she will turn to you first.
If she does go ahead with the relationship, you may just have to deal with it until she figures it out for herself. If you feel counseling would help you cope better, that might be a way to help you deal with the stress of the situation. Keep in mind that your daughter would not be the first child to go in a different direction at that age. Oftentimes, it's just making the mistake that helps kids learn that Mom and Dad where right in the first place.
I hope this has helped you,