I know that's a short period of time but he's one of my brother's best friends and my brother and I are very best friends! I completely trust my brother (48m) and he completely trusts my partner.

You sound like a very naive teenager tbh. You're only 3 months in, and no matter how good your bf gets along with your brother, at this stage, there's no guarantee for you to be compatible longterm.

g. I am definitely in love with him a

You're infatuated at this stage, it's the earliest stage of the honeymoon period.

I feel confident that my partner and I won't be breaking up anytime soon if ever. I'm pretty sure I could definitely marry him.

Most people think that in the early honeymoon stage. Still lots of them end up breaking up with their partner.

One question I do have is how becoming a parent might change a relationship for better or worse? Is it even possible to move this quickly and be successful partners and parents? I

If you go through with this, get into premarital counseling (individual and as a couple), and make sure you discuss worst case scenarios. If you have a kid, and you separate....what happens then? And how will it impact the child?