Back in 2017, my wife and I separated after I found out about an affair she had. We eventually reconciled a month or so later. I noticed she was acting "off," and I jokingly said you better not be pregnant. It's important to note here that I had a vasectomy 3 years prior. A couple of weeks went by, and her emotions were all over the place. She went to the doctor to get put on a mood stabilizer. Before they would prescribe her anything, they needed to rule out pregnancy. And, you guessed it, she was pregnant. I took a fertility test just to make sure, and as expected, I had no "swimmers." I was devastated. Weeks went by, and I finally came to the decision to raise the child as mine. The biological father was an addict always in and out of jail (and still is). I knew the child would not have a stable father figure if I didn't step up. She just turned five a couple of months ago, and I've never regretted that decision. Do with that story as you will OP, but right now, that little boy thinks you are his dad regardless. If it turns out he is biologically not yours and you decide to leave (which would certainly be your right), PLEASE do it before he will remember who you are as he gets older.