Question: How do you create an obstacle between a guy who loves someone he cannot have but will do anything to have her?
This is a story of unrequited love in a character who believes in his will.Answer:
The guy sounds like a monster.
Seriously, there are only two options for an unrequited lover who won't take no for an answer. Either he becomes a monster who tries to force his will on another person (and God help the other person), or he is forced to examine himself and change his ways so that he becomes someone who is worthy of the relationship.
For instance, you say he will do anything to win this woman's love. But can he do it without caring about getting anything in return?
Or can he learn to respect her situation, feelings, etc. and so become someone who can overcome the obstacles, or someone she can fall in love with?
Or perhaps in the process of self-examination and change he matures to the point that he gives up his infatuation/fantasy and finds a better relationship with someone that is build on something more substantial.
In such stories, the obstacles are often the result of ego -- whether it's the arrogance of the man trying to fulfill his fantasy about someone, or the jealousy of someone in the woman's life who is keeping her from her true love. Sometimes pride is the problem, or bitterness, or jealousy. The point is that ego creates dysfunctional relationships that need to be rebalanced.