Am I the jerk for not wanting to adopt my dying ex-girlfriend's child?

I'm a 31 year old male and I met my ex-girlfriend who's 29 on a dating app seven years ago.

She had a son six months old at the time. She was with multiple guys and ended up pregnant.

She still doesn't know who the biological father is, but it wasn't that much of an issue since she

seemed like a great person and we had a lot in common. After a few weeks of chatting and talking

online we went on a first date and had a great time. After that we just started hanging out

whenever she could and shortly after she introduced me to her son. A few months into our relationship

we moved in together to save money since both of us were renting at the time. I started helping

her take care of her child whenever I could and we really just grew fond of each other.

He even started calling me papa and we just went along with it since my girlfriend didn't mind.

Almost five years into our relationship she told me that she wants to break up because I

became a boring person and not an active person like I used to be. We used to go on hikes and

travel around the country on the weekends and also that I work too much now. It was a rough time

after that and I had a hard time accepting it although not as hard as having to explain to a five

year old that he'll no longer be seeing his papa. But I managed to get over it after a few months

found a better job that allowed me to work remotely and had a lot of free time so I managed to explore

a few other countries. A few days ago I got a call from my ex she said that she is sick and in

the hospital they removed one of her breasts but she recently found a tumor in her other breast

and will need to have her removed as well. She scared that she might die if it doesn't work out

and asked me if I would be willing to become her son's legal guardian and adopt him since she has

no one else to ask. I live a different lifestyle now. I travel a lot and I invest in myself so I told

no I can't do that. She told me that her son misses me and would love to see me but I said no

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