My (35f) fiance Ben (35m) has a 10 year old son with his ex Sara. They split about 7 years ago when Ben caught her cheating. At that same time, Ben also found out that another man claimed he was the father of their son. Sara told Ben this wasn't true and they moved on. Ben confessed to me one night sobbing that he wrestles with that his son may not be his. As his son gets older, he doesn't look like him. He's afraid to find out if his son isn't his, because he doesn't know how it will affect them.

Their coparenting relationship can be strained sometimes, particularly with custody (parents live 15 mins apart). Sara is a bit of a control freak and likes things her way which impacts Ben's time with his son. Weekends together are cut short because Sara has plans or Ben can't see his son at all during spring break because of play dates. Requests for after school ice cream are denied. Ben doesn't get any additional time with his son during the summer (Sara declines).

An official custody agreement is be needed so that Ben could get all his time with his son. As I am thinking more about it, I think Ben should have a paternity test on his son. I think that if court is going to get involved and potentially get ugly, Ben should be fully informed. I recognize that it's not my child/relationship however this is also my life I am sharing with Ben and I too should be fully informed. Would I be the asshole for asking for a paternity test so that we can address custody of his son?

EDIT: this is not a surprise to Ben, we discussed this before about a paternity test. He admitted being afraid of the results and having the desire to walk away if it's not his son. I will support Ben whatever he decides to do and will love and treat his son the same.

TL;DR fiancé son has questionable paternity, would I be the asshole asking fiancé to confirm paternity before trying to battle custody?