Divorced reluctant father - Mother is remarrying - I want to reduce my involvement

Sorry in advance - this is long.Let's start with a little background -We got divorced when my son was less than a year old. His mother got primary custody and she is great, she's very attentive, loving, and enthusiastic about motherhood and doing everything she can for him. Honestly, all around a fantastic parent.It's been a couple years now, he just turned 3.I've been faithful in paying child support, and I've mostly stayed on top of visitation because I know kids need a father figure. We currently spend an hour and a half together twice a week, and have had a few overnights since he turned three (that's when overnights started in the custody arrangement). His visits always go really well, he has a great time and is always excited to come over, but since the beginning I've just felt like I'm just going through the motions.He's a smart, delightful kid, his demeanor and mannerisms remind me so much of myself, he's exactly the son I would have hoped for, but to be honest, I just don't want to be a father. I feel like an outsider. Everything I've done up to this point, I've done because I know it's my responsibility, but I just don't feel the way I think a parent ought to feel. I want to do the right thing by him, but I don't think I can sustainably force myself to feel enthusiastic about fatherhood, which means I fear I'm on track to be some kind of half-hearted uncle-dad. I don't want to do that to myself and I don't want to do that to him.His mother has expressed more than once that she doesn't really care whether I actually do visitation or not, she'd rather have him to herself. She's made it clear that my presence in her life is an inconvenience, and she would have preferred to be a widow single-parent rather than a divorcee co-parent.Now that his mom is getting remarried to a nice guy who he's become close with, it kinda feels like he has a chance to grow up in a normal-feeling family situation with his mom and step-dad, and I can't help thinking that maybe I should just let them do that without me.So here's the question - given that I'm currently an involved, but arguably not great or eager dad - would I be doing some long-term harm to my son by stepping away and leaving him to grow up with his mother and step-dad instead? Possibly moving to another state. Possibly talking to his mom about offering to let her new husband adopt my son in the future. (I think she'd really love that)Please take it easy on me, this is a hard topic to approach because every time I think about it I feel like some kind of rotten, heartless sociopath. I need help sorting this out and don't feel comfortable bringing it up with any of my friends or family.Looking for any advice you can offer. This has been on my mind a lot recently and it'd really help to talk it through with someone.Thanks. via /r/Parenting https://ift.tt/2SO8Kdy