Can i be finally united with him in my next life?
Will my parent be the same in my next life?
For people to meet again in future lives there must be conditions favorable to that coming again together. Things conducive to it are having same beliefs, same generosity, same wisdom, same virtue, similar faculties & behavior, apples don't fall far from the tree in general.
To give an example if two people behaved like dogs and cultivated that behavior successfully, they would be born in the company of dogs and probably together still because their minds incline to it and conditions are favorable.
Coming back together may occur in circumstances where conditions such as gender are changed and one may become a dog, a horse or whatnot.
I love to be a doctor be part of medecins sans frontiers and cure people for free but in this life didn't succeed as my iq was not perfect in many fields in study.
Maybe you can and maybe you can't. This again depends on how you cultivate your mind. As an example if a dog looks up to humans and imitates their good behaviors, then even the dog can attain the human state, how much more a human who imitates the behaviors of wise people.
can't stop thinking of him every single day of my life.
When we think about something it is recognized and explored as a basis for pleasure, pain or equanimity.
Thoughts associated with pleasure are pleasant and inflame the mind, nothing is as obsessive as thoughts of infatuation with the sexuality.
Whatever you give frequent attention will become the inclination of the mind as the mind adapts to work efficiently. The pathways by which thoughts travel become developed & strengthened due to frequent use.
One can think of this as sending an electric current through wires, the charge will simply follow the path of least resistance and activate those structures.
If you give attention only to a positive aspect of an idea then that perception of beauty will be given a lot of attention and it will become the dominant perspective on it, the perception of beauty will become established and the perception of drawbacks will be given little to no weight & entertainment. This person will become "intoxicated" with beauty, due to not paying mind to the unattractiveness, then will behave irrationally seeing beauty in what is essentially not worthy of such regard & pursuit.
This site has many questions about the removal of distracting thoughts and development of good mental behavior.