Hi Rain. You're better off without him I'm sure. Babies reach milestones at their own pace I really wouldn't worry too much at this point. You may wake up one day and he'll be doing EVERYTHING at once.
Hi! Welcome! Have you talked to his pediatrician about it? Babies do things at their own pace, and I think 8 months is fine to start sitting. But you should talk to the doc if your concerned. He/she will be able to put your mind at ease I'm sure!
Welcome! My DD is almost 8 months old too, and she is a bit behind on some of the milestones as well. She does great with the verbal stuff and fine motor skills, but her gross motor skills are a mess. She isn't sitting on her own for more than a few seconds, only rolled a few times (hates being on her tummy), and I doubt she will crawl anytime soon (or ever perhaps!). If you are super concerned, it may be worth a visit to the pedi, but like PPs said, all babies are so different.
Re: Intro