I decided to make this ask rebloggable in case someone might like to share their own theory
Unfortunately, I don’t know enough about Spiderman to speculate too deeply but I’d say it’s safe to say he has good reason to have some daddy issues.
Peter lost his father when he was still very young (canon has varied about the exact age) and lost the father figure he had in Uncle Ben in an event he blames himself for. It is because of this guilt and dedication to his uncle that he becomes Spiderman, and although he desperately wants a normal life continues to be him. Peter, either by design or fate, places himself under the authority of very powerful men he looks up to: Reed Richards, Steve Rogers, etc.
Deadpool also has some major daddy issues. His own father was abusive and neglectful and Wade began idolizing superheroes from young age (also Steve Rogers and even Spiderman himself) Wade agonizes over acceptance and praise from anyone and everyone and eventually pseudo-married Cable, a much older man who treated him in a very fatherly manner but eventually left him.
Both Peter and Wade hold their father figures in high esteem and have built identities around being the abandoned child. Ideologies aside, I think this would be the biggest obstacle in their relationship; each would unadmittedly look for guidance and domination in the other while being too prideful to admit and, in the end, not really knowing how to provide it anyway.
I know some people might disagree with this because Deadpool is often interpreted as being a physically and emotionally dominant partner to Peter, but in canon he is extremely, extremely submissive with his sexual partners.