I'd like to join Mary in welcoming you back though sad at the circumstances.
As is obvious fate dealt you hard hand, a wife who dies of melanoma and a teen daughter turned into a para due to an unfortunate act. Just helping her would be a a pretty full job, and if like many young ladies she feels her condition renders her impossibly unattractive you have to deal with all that too.
Then you met someone else and again felt that depth of feeling you had before -but now you know it can be such a fragile state.
So what do you do, you try, even without thinking to preserve that feeling , hypersensitive to things that might be precursors of less love, needy though sex as reassurance, accusatory and jealous.
I'm sorry to be blunt, however I'm sure you know these things already. I'm sure you also know the way a loving partner behaves, and it is none of those hings, it is you giving, reassuring, you understanding other's needs ... I'm sure you can think of many more.
Again to be blunt you have the release the bonds of need, allow the person to remain becuse they want, need, can rely upon and enjoy it themselves with you.
Frankly I would think you lucky your partner has remained and tried for you - you have found a person worth making sacrifices for.
Most parents go though this, kids have permission and sometimes help, to leave home, hopefully if it has been a loving relationship they will be there for you -even at a distance -all their lives.
So how do you change? 2 years of your own efforts have not worked, so I would suggest you seek professional medical help to teach you to reduce your anxieties.
Could you see your GP in a long consultation, explain you original grief and anxieties anxieties seem to have combined and ask for help before you alienate the one you love? It may be your current actions are not just based on the loses you describe, but other factors too -so the help has to be skilled.
Please come back and say what you think?