Oh sweetie, you have shouldered so much in the last five years. You are so strong!
Though I haven't been through your exact situation, I have been in a similar place and I can't recommend counseling enough. You are coming off a string of tragedies that most don't see in a lifetime, much less two years. Whether you go to a grief support group, individual counseling or a weight loss support group, I think you could really benefit from taking time to process what's happened in your life.
I hope you don't take this the wrong way, but it alarms me a little that your FI wants to rip you away from your family home. Especially after all you have been through. I don't know, it just seems like he should be supporting you, not forcing you to do something you don't want to do. Plus you seem to jump from relationship to relationship without really thinking things through (again, not judging, I have so been there) and I think you need to take a step back before you get married and move away.