I've been married to my wife for 10 years, and she has a son from a previous relationship. We have a solid relationship, but I’ve never felt comfortable with him calling me “Dad” because I don't want to step on his biological father’s toes. His dad is in the picture, though not consistently. 2/3

Yes

Yes, you’re the asshole. The child is comfortable with you and secure enough in your relationship that he wants to call you dad. Unless you’re planning to ditch the family, be a dad.

There are so many names for “dad”. You could come up with another “dad” name together that works for both of you.

My son tells everyone that his bio-dad is his “father” but my now ex-husband, who has been in his life since he was 3 (he just turned 18) is his dad and they are very close. We just divorced in June but even so, it his dad not his “father” who will be helping him pay for college and do many other things as he heads into adulthood. So you need to realize that your stepson wanting to call you dad is a REALLY big deal in the sometimes tricky way kids have of wording things.

U are an a-hole!!