Thank you for writing about this difficult situation. There are several issues here that are intersecting with your question. Let me respond by trying to sort them as I see them.
First, his lack of forthrightness in not telling you about his obligations is huge. This means that the unresolved components of his life, the greatest source of conflict for the two of you and likely the greatest ongoing clash for the rest of your lives if you stay together, was not revealed for very selfish reasons. You found out the most important intimate relationship in your life was built on a lie. This was not a fair encounter. Ask yourself the question: Would you have hidden such a situation from him? This will reveal if there is a fundamental difference between the two of you. If you would have kept it secret then the two of you are cut from the same cloth. If not, you have to acknowledge the fact that he was willing to hide something from you because he knew it had the potential for making him unacceptable. You are now willing to keep secrets from those you love because you are embarrassed, and he isn’t willing to tell his family. Both of you are now keeping secrets. Add to this the fact that he didn’t tell you, and may not have. This brings up the question of his ex-girlfriend’s motivation and needs in this situation. Are you willing to deal with that? More importantly you must ask why you’d want to.
Secondly, it is clear he hasn’t dealt with this problem adequetly, and now has a legal issue. By not telling you, and not dealing with her it has gotten worse. If you stay with him these issues will become yours. Do not minimize this. This is an ongoing concern that will affect your lives in a profound way. You must ask if this is something you are willing to take on. Again, more importantly, ask yourself why you would want to.
Finally you are asking if staying with him is going to ruin your life. Is this a risk you are willing to take? You already know this will be a major financial, legal and emotional issue to cope with, and are asking if these features could mess up your life. These are his problems and they are significant. He has not dealt with them in a straightforward way, and had kept the truth of who he is from you. It seems to me he has a lot to cope with before he can be fully ready for a relationship. His primary strategy seems to be not to deal with the most important concerns in his life. So far there is little you have told me to suggest he has changed.
I would encourage you to seek some individual therapy from the university counseling center to begin coping with the decision in front of you. I am glad you reached out here to get some feedback. It is now time to reach out to a counselor to gain some clarity about your decision.
Wishing you patience and peace,