"I have had more life experience in my 20 years of life than post people will ever experience" that statement manages to be both arrogant and ignorant! You're assuming those of us responding haven't had similar experiences to you and therefore don't understand why you THINK you have a lot of life experience and we're wrong to say you're immature in some ways.
Certainly in my case, and by law of averages it's likely to be true of others too, you are WRONG!
I grew up in an abusive home with an alcoholic, violent parent. I left home at 17 as a result and first fell pregnant at 18 (we'd been together almost 3 years. Pill failed, as it occasionally can even with correct use, what I wish someone had told me was that around this age fertility can be particularly high and so 2 methods of contraception really is best. I also had an at that time undx condition which possibly meant the pill was less reliable but again I had no knowledge of this) my own pregnancy ended in mc, but if it hadn't I was well aware I WASN'T particularly mature purely by having a shit childhood.
Instead I was concerned because I'd not been set a good example of parenting, and as an 18 year old living in a bedsit working a low paid job (most jobs before you're 21 are low paid even now, even if not nmw) was not in the best position to be a parent.
I don't know what decision I'd have made if the decision weren't taken out of my hands by events but certainly abortion and adoption would have been options I'd have at least considered.
Having a shit/non existent childhood == maturity, indeed it can mean the opposite often.
"We both know how to avoid being a bad parent" most parents even, perhaps especially the good ones recognise that while they tend to avoid the mistakes their parents made, they often end up making different ones by default. Eg those brought up by too strict parents being too lax on discipline with their own kids.
See this poem
www.poetryfoundation.org/poems/48419/this-be-the-verse
NO parent is perfect but quite honestly someone who THINKS they will be a better parent purely because the arrogantly think they have more knowledge/experience than others is far more likely to fuck up parenthood than one who is aware of their faults and disadvantages and willing to be open to advice and information from those who have more experience and knowledge.
"I have so much experience from looking after him all the time. I have strong mothering instincts anyway, which people have always said and I love children."
I'm the eldest of 3 siblings, a ton of cousins and I've been looking after other people's kids "officially" since I was 14, I was a nanny & a nurse before becoming a parent and I've been a childminder since - caring for other people's children is NEVER the same as being a parent.
The emotional dynamic, the relationship, the exhaustion, the responsibility is on a COMPLETELY different level. You seem very stubbornly unwilling to acknowledge this - being like that, expecting that you'll find it relatively easy because of all the "experience" you have? Actually puts you at more risk of finding it difficult - because you're setting yourself up for a fall!
Because WHEN you hit a situation that it's impossible to experience as a carer for others children, you will be thrown.
"The perfect parent is the one that doesn't yet have children"
His parents have not handled several issues at all well from what you say, you don't have to tolerate rudeness or aggression from them (including verbal) but I really do think given the likely outcome here (the two of you separating, him moving back to parents, your child staying there during his contact time) you need to find some way to handle them, communicate with them, that isn't simply ignoring them. Because unfortunately I think it highly likely they will become involved in your child's care and you need to be able to communicate with them with regard to your child's needs, routine etc.
It's far from ideal but unfortunately it's still very difficult to prove emotional abusiveness to a point that a court would agree with you, if you and your partner were to split, that he shouldn't have contact at his family's home.
Hopefully this will change but it takes a long time for these changes to be made societally/legally.